[DRIVERS] irqchip: Add versatile fpga-based interrupt controller driver

The VersatilePB and VersatileAB platforms have nested PICs where the
primary PIC is PL190 (Vectored Interrupt Controller) and secondary
PIC is FPGA-based interrupt controller.

This patch adds driver for Versatile FPGA-based interrupt controller.

Signed-off-by: Anup Patel <anup@brainfault.org>