target/arc: introduce breakpoint functionality

target/arc: introduce breakpoint functionality

With this patch we introduce set/unset breakpoints
routines and add/remove bp handlers.
Currently soft breakpoints are only supported.

Changes since v1:
* Change if-statement in arc_remove_breakpoint
* Squash changes from http://openocd.zylin.com/#/c/5641/
  in this commit to fix build.

Change-Id: Ib10ccdb02fd1606e4f407f012b1bee106a8ffccd
Signed-off-by: Evgeniy Didin <didin@synopsys.com>
Reviewed-on: http://openocd.zylin.com/5641
Tested-by: jenkins
Reviewed-by: Oleksij Rempel <linux@rempel-privat.de>