Patch from George G. Davis

Adds support for Thumb ld/st alignment fault fixups via conversion of
Thumb ld/st instruction forms into equivalent ARM instructions and
reusing ARM alignment fault handler for Thumb instructions. This
implementation was inspired by and initially based on the algorithm
found in gdb/sim/arm/thumbemu.c.

I've backed out the silly 'T' suffix on PC in this version as requested
by RMK. At this point, I prefer to avoid making any of the other changes
discussed, e.g. dump_instr() for bad instruction cases, in order to get
the basic Thumb support change committed.

Thanks!

Signed-off-by: George G. Davis
Signed-off-by: Russell King