ARM: ep93xx: convert to MULTI_IRQ_HANDLER

Now that there is a generic IRQ handler for multiple VIC devices use it
for ep93xx to help building multi platform kernels.

Cc: Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ryan Mallon <rmallon@gmail.com>
Signed-off-by: Jamie Iles <jamie@jamieiles.com>