ARM: integrator/versatile: consolidate FPGA IRQ handling code

Consolidate the FPGA IRQ handling code.  Integrator/AP and Versatile
have one FPGA-based IRQ handler each.  Integrator/CP has three.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>