ARM: dts: TS-4800: add FPGA's IRQ controller support

Enable FPGA's IRQ controller. It is in charge of dispatching interrupts
generated by IPs in the FPGA. The SoC is notified that an interrupt
occurred through a GPIO.

Signed-off-by: Damien Riegel <damien.riegel@savoirfairelinux.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>