MIPS: JZ4740: use generic plat_irq_dispatch

MIPS: JZ4740: use generic plat_irq_dispatch

Make use of the generic plat_irq_dispatch function introduced by commit
85f7cdacbb81 "MIPS: Provide a generic plat_irq_dispatch", in order to
reduce unnecessary code duplication.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Lars-Peter Clausen <lars@metafoo.de>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: Brian Norris <computersforpeace@gmail.com>
Patchwork: https://patchwork.linux-mips.org/patch/10138/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>