Use specific logging functions instead of a generic
bt_printk function can save some text.

Remove now unused bt_printk function.
Add compatibility BT_INFO and BT_ERR macros.

(compiled x86 and defconfig with bluetooth and all bluetooth drivers)

$ size net/bluetooth/built-in.o*
   text	   data	    bss	    dec	    hex	filename
 381662	  20072	 100416	 502150	  7a986	net/bluetooth/built-in.o.allyesconfig.new
 382463	  20072	 100400	 502935	  7ac97	net/bluetooth/built-in.o.allyesconfig.old
 126635	   1388	    132	 128155	  1f49b	net/bluetooth/built-in.o.defconfig.new
 127175	   1388	    132	 128695	  1f6b7	net/bluetooth/built-in.o.defconfig.old

$ size drivers/bluetooth/built-in.o*
 127575	   8976	  29476	 166027	  2888b	drivers/bluetooth/built-in.o.allyesconfig.new
 129512	   8976	  29516	 168004	  29044	drivers/bluetooth/built-in.o.allyesconfig.old
  52998	   3292	    156	  56446	   dc7e	drivers/bluetooth/built-in.o.defconfig.new
  54358	   3292	    156	  57806	   e1ce	drivers/bluetooth/built-in.o.defconfig.old

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>