Fixes sparse warnings:

  arch/mips/jz4740/irq.c:63:6: warning: symbol 'jz4740_irq_suspend' was not declared. Should it be static?
  arch/mips/jz4740/irq.c:69:6: warning: symbol 'jz4740_irq_resume' was not declared. Should it be static?

Also, I've seen some elusive build errors on my automated build test
where JZ4740_IRQ_BASE and NR_IRQS are missing, but I can't reproduce
them manually for some reason. Anyway, mach-jz4740/irq.h should help us
avoid relying on some implicit include.
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8724/Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>