microblaze: Don't mark arch_kgdb_ops as const.

Other architectures don't do it, and it conflicts with the extern'd definition
in include/linux/kgdb.h.

The patch fails checkpatch but it reflects current
functions declaration and solved compilation error.

Signed-off-by: Graeme Smecher <gsmecher@threespeedlogic.com>
CC: Michal Simek <monstr@monstr.eu>
CC: linux-kernel@vger.kernel.org
Signed-off-by: Michal Simek <michal.simek@xilinx.com>