arm: Move the set_handle_irq and handle_arch_irq declarations to asm/irq.h

This patch prepares the removal of <asm/mach/irq.h> include in the
GIC and VIC irqchip drivers.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Marc Zyngier <marc.zyngier@arm.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Rob Herring <rob.herring@calxeda.com>