mips32, add generic scan 32 function

Will be used later, allow queuing all needed scans in a pracc
access. This makes faster execution with ftdi based adapters
working in sync with pracc.
Added now because the overall code is shorter.

Change-Id: Ib32b89307b75785f88870db8d7c9255dc5bbd426
Signed-off-by: Salvador Arroyo <sarroyofdez@yahoo.es>
Reviewed-on: http://openocd.zylin.com/4005


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