Indentation should be done with spaces, not with TABs, in the SH4 subsystem

There are still a lot of old files in the QEMU SH4 code base that use TABs for indentation instead of using spaces in these files here:

 hw/intc/sh_intc.c
 hw/sh4/sh7750_regs.h
 hw/sh4/r2d.c
 hw/sh4/sh7750.c
 hw/sh4/sh7750_regnames.c
 linux-user/sh4/termbits.h
 target/sh4/cpu.h
 target/sh4/op_helper.c
 target/sh4/translate.c
 target/sh4/helper.c

The TABs should be replaced with spaces, to make sure that we have a consistent coding style with an indentation of 4 spaces everywhere.