ARM: versatile: convert to MULTI_IRQ_HANDLER

Now that there is a generic IRQ handler for multiple VIC devices use it
for versatile to help building multi platform kernels.

Cc: Russell King <linux@arm.linux.org.uk>
Tested-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Jamie Iles <jamie@jamieiles.com>