m68k: 68000 strict alignment requirements not emulated correctly

Description of problem

Unaligned accesses should cause an address error on the 68000 but apparently currently don't.

Steps to reproduce

1. Create a 68000 based QEMU machine to port u-boot/linux
2. Get u-boot/linux working perfectly on your QEMU machine
3. Copy kernel over to your real 68000 hardware
4. Notice that the kernel doesn't work
5. Spend a day adding inline assembly all over the kernel to work out where the real hardware is locking up
6. Find that the issue is probably memmove() being called with an unaligned src pointer:

C level..

Breakpoint 1, memmove (n=215, src=0x2059df <printk_shared_pbufs+215>, dest=0x2059ee <printk_shared_pbufs+230>) at ../arch/m68k/lib/memmove.c:152
152                             *--sdest = *--ssrc;
(gdb) bt
#0  memmove (n=215, src=0x2059df <printk_shared_pbufs+215>, dest=0x2059ee <printk_shared_pbufs+230>) at ../arch/m68k/lib/memmove.c:152
#1  memmove (dest=<optimized out>, src=<optimized out>, n=<optimized out>) at ../arch/m68k/lib/memmove.c:10
#2  0x000265b6 in record_print_text (r=<optimized out>, syslog=<optimized out>, time=<optimized out>) at ../kernel/printk/printk.c:1472
#3  0x00027be6 in printk_get_next_message (pmsg=<optimized out>, seq=<optimized out>, is_extended=<optimized out>, may_suppress=<optimized out>) at ../kernel/printk/printk.c:2952
#4  0x00027e5a in console_emit_next_record (cookie=0, handover=0x1d9e37, con=0x1edf14 <early_con>) at ../kernel/printk/printk.c:3019
#5  console_flush_all (do_cond_resched=false, next_seq=0x1d9e38, handover=0x1d9e37) at ../kernel/printk/printk.c:3118
#6  0x00027fc8 in console_unlock () at ../kernel/printk/printk.c:3187
#7  0x00028a04 in vprintk_emit (facility=0, level=<optimized out>, dev_info=0x0, fmt=0x1bd051 "\0016printk: %s%sconsole [%s%d] enabled\n", args=0x1d9e98) at ../kernel/printk/printk.c:2359
#8  0x00028a26 in vprintk_default (fmt=0x1bd051 "\0016printk: %s%sconsole [%s%d] enabled\n", args=0x1d9e98) at ../kernel/printk/printk.c:2374
#9  0x00028c22 in vprintk (fmt=0x1bd051 "\0016printk: %s%sconsole [%s%d] enabled\n", args=0x1d9e98) at ../kernel/printk/printk_safe.c:45
#10 0x0019d016 in _printk (fmt=0x1bd051 "\0016printk: %s%sconsole [%s%d] enabled\n") at ../kernel/printk/printk.c:2384
#11 0x0002857e in register_console (newcon=<optimized out>) at ../kernel/printk/printk.c:3693
#12 0x001fbf1e in register_earlycon (match=<optimized out>, buf=0x0) at ../drivers/tty/serial/earlycon.c:161
#13 setup_earlycon (buf=<optimized out>) at ../drivers/tty/serial/earlycon.c:212
#14 0x001fbf72 in param_setup_earlycon (buf=0x2009e9 <tmp_cmdline+9> "mc68ez328,0xfffff900") at ../drivers/tty/serial/earlycon.c:244
#15 0x001f1102 in do_early_param (param=0x2009e0 <tmp_cmdline> "earlycon", val=0x2009e9 <tmp_cmdline+9> "mc68ez328,0xfffff900", unused=0x1b96c6 "early options", arg=0x0)
    at ../init/main.c:744
#16 0x00017eac in parse_one (handle_unknown=<optimized out>, arg=<optimized out>, max_level=<optimized out>, min_level=<optimized out>, num_params=<optimized out>, params=<optimized out>, 
    doing=0x1b96c6 "early options", val=0x2009e9 <tmp_cmdline+9> "mc68ez328,0xfffff900", param=0x2009e0 <tmp_cmdline> "earlycon") at ../kernel/params.c:154
#17 parse_args (doing=<optimized out>, args=0x2009fe <tmp_cmdline+30> "console=ttyDB0 root=/dev/mmcblk0p2 rootfstype=squashfs rootwait", params=<optimized out>, num=<optimized out>, 
    min_level=<optimized out>, max_level=<optimized out>, arg=<optimized out>, unknown=<optimized out>) at ../kernel/params.c:189
#18 0x001f13ea in parse_early_options (cmdline=0x2009e0 <tmp_cmdline> "earlycon") at ../init/main.c:754
#19 0x001f1420 in parse_early_param () at ../init/main.c:769
#20 0x001f1570 in start_kernel () at ../init/main.c:908
#21 0x000004b8 in _clear_bss () at ../arch/m68k/dt/head.S:95
#22 0x00000000 in ?? ()

Asm level:

152                             *--sdest = *--ssrc;
   0x0019bed8 <+324>:   movel %a1,%d2
   0x0019beda <+326>:   subql #2,%d2
   0x0019bedc <+328>:   movel %a2,%d1
   0x0019bede <+330>:   subql #2,%d1
=> 0x0019bee0 <+332>:   movew %a1@(-2),%a2@(-2)

This is a word store so needs to be aligned but a1 isn't aligned so we should get an address error:

(gdb) print/x $a1
$3 = 0x2059df
(gdb) print/x $a2
$4 = 0x2059ee

7. Check QEMU source code to work out why it doesn't crash the cpu at the same place.
8. Notice it doesn't seem to check the alignment.

Additional information