mips32: add new functions mips32_configure_ibs and _dbs

mips32: add new functions mips32_configure_ibs and _dbs

Split function mips32_configure_break_unit
to mips32_configure_ibs and mips32_configure_dbs
to make code more readable.

This will probably make work easyer with differnet EJTAG versions.

Change-Id: I666f949fd7bc3656bdf75e7bcaadb164f15855dd
Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
Reviewed-on: http://openocd.zylin.com/1463
Tested-by: jenkins
Reviewed-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>