ARM: 6538/1: Subarch IRQ handler macros V3

Per subarch interrupt handler macros V3.

This patch breaks out code from the irq_handler macro
into arch_irq_handler and arch_irq_handler_default.

The macros are put in the header file "entry-macro-multi.S"

The arch_irq_handler_default macro is designed to be
used by irq_handler in entry-armv.S while arch_irq_handler
is suitable for per-subarch use.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>