mips32, add realloc code

If max_code is reached realloc memory. If fails to realloc
the error is propagated and every call to pracc_add() returns
immediately. The exec function logs the error.

Change-Id: Idd4ed9d9b8b19b7d6842d0bc5ebb05f943726705
Signed-off-by: Salvador Arroyo <sarroyofdez@yahoo.es>
Reviewed-on: http://openocd.zylin.com/4020


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