[MC][ARM] add .w suffixes for BL (T1) and DBG

F1.2 Standard assembler syntax fields
describes .w and .n suffixes for wide and narrow encodings.

arch/arm/probes/kprobes/test-thumb.c tests installing kprobes for
certain instructions using inline asm.  There's a few instructions we
fail to assemble due to missing .w t2InstAliases.

Adds .w suffixes for:
* bl  (F5.1.25 BL, BLX (immediate) T1)
* dbg (F5.1.42 DBG T1)

Reviewed By: DavidSpickett

Differential Revision: https://reviews.llvm.org/D97236