mips32: add micromips breakpoints support

Breakpoint setting based on length (kind) only.
Added 16bit aligned 32bit software breakpoints
support and same filtering before setting
breakpoint.
Set the required isa bit in hardware breakpoints.
Drop the isa bit in software breakpoints.

Change-Id: I7020f27be16015194b76f385d9b8e5af496d0dfc
Signed-off-by: Salvador Arroyo <sarroyofdez@yahoo.es>
Reviewed-on: http://openocd.zylin.com/4124


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