ARM: dts: keystone-k2g: Add keystone IRQ controller node

Add the Keystone IRQ controller IP node on K2G SoC. This allows the
ARM CorePac core to receive interrupts from remote processor devices
(eg: DSP) on the SoC.

The IP is identical in functionality to that of the equivalent
nodes on existing K2 SoCs. The only difference is the ARM INTC
interrupt id/event number.

Signed-off-by: Andrew F. Davis <afd@ti.com>
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>