JIT: Combine shift & sub for monitor unlock.

Optimize monitor unlock for ARM Thumb2 JIT.
Monitor unlock performs a logical shift left
and sub, replace it with a sub capable of
performing the shift in the same instruction.

This improves performance for usecases involving code
executing in Dalvik.

Change-Id: Iaf062d750c3bc941926f3c3b8a64dc9c7984a477
Signed-off-by: Patrik Ryd <patrik.ryd@stericsson.com>