microblaze: Enable KGDB in defconfig

Enable KGDB in defconfig to be sure that support
is regularly compiled.
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/microblaze/configs/mmu_defconfig

-CONFIG_EXPERIMENTAL=y
 CONFIG_SYSVIPC=y
 CONFIG_POSIX_MQUEUE=y
 CONFIG_FHANDLE=y
@@ -81,6 +80,9 @@ CONFIG_DETECT_HUNG_TASK=y
 CONFIG_DEBUG_SLAB=y
 CONFIG_DEBUG_SPINLOCK=y
 CONFIG_DEBUG_INFO=y
+CONFIG_KGDB=y
+CONFIG_KGDB_TESTS=y
+CONFIG_KGDB_KDB=y
 CONFIG_EARLY_PRINTK=y
 CONFIG_KEYS=y
 CONFIG_ENCRYPTED_KEYS=y