MIPS: KGDB: fix kgdb support for SMP platforms.

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>