mips32, add microMips instruction subset

Only reencoded MIPS32 instructions. Added some instructions
for crc code. Micromips isa in debug mode is only needed for
pic32mm cores. Pic32mz seems that only works with MIPS32
isa when in debug mode.

Change-Id: I07059e153a7000ea9204f20b6b37edf6a7623455
Signed-off-by: Salvador Arroyo <sarroyofdez@yahoo.es>
Reviewed-on: http://openocd.zylin.com/4022


Tested-by: jenkins
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>