[ARM] 3645/1: S3C2412: irq support for external interrupts

Patch from Ben Dooks

Move the decoding of the IRQ_EXT4 and above out of
the entry macro, and into an chained irq handler
as the EXTINT registers move depending on the CPU
being used.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>