MIPS: KGDB: fix kgdb support for SMP platforms.

KGDB_call_nmi_hook is called by other cpu through smp call.
MIPS smp call is processed in ipi irq handler and regs is saved in
 handle_int.
So kgdb_call_nmi_hook get regs by get_irq_regs and regs will be passed
 to kgdb_cpu_enter.

Signed-off-by: Chong Qiao <qiaochong@loongson.cn>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: QiaoChong <qiaochong@loongson.cn>

arch/mips/kernel/kgdb.c

@@ -33,6 +33,7 @@
 #include <asm/processor.h>
 #include <asm/sigcontext.h>
 #include <linux/uaccess.h>
+#include <asm/irq_regs.h>
 
 static struct hard_trap_info {
 	unsigned char tt;	/* Trap type code for MIPS R3xxx and R4xxx */
@@ -214,7 +215,7 @@ void kgdb_call_nmi_hook(void *ignored)
 	old_fs = get_fs();
 	set_fs(KERNEL_DS);
 
-	kgdb_nmicallback(raw_smp_processor_id(), NULL);
+	kgdb_nmicallback(raw_smp_processor_id(), get_irq_regs());
 
 	set_fs(old_fs);
 }