This makes the newer v2 api behave as per the v1 api, eg. single stepping
masks all interrupts.
A better long term solution is to use same behaviour as a cortex-m3
target, see CORTEX_M3_ISRMASK_AUTO.
Change-Id: Iaf9f9adf225cf274faaac938050bb996582aa98f
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/621
Tested-by: jenkins