Blackfin: kgdb: disable interrupt when single stepping in ADEOS

When ADEOS and kgdb are both enabled, single step in linux kernel may be
scheduled to Xenomai core after return from interrupt handlers.  This
blocks gdb continue operation after a break point is hit.  So, disable
interrupt when running gdb single step.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>