ARM: mstar: Add interrupt controller to base dtsi

Add the IRQ and FIQ intc instances to the base MStar/SigmaStar v7
dtsi. All of the known SoCs have both and at the same place with
their common IPs using the same interrupt lines.

Link: https://lore.kernel.org/r/20201002133418.2250277-3-daniel@0x0f.com
Signed-off-by: Daniel Palmer <daniel@0x0f.com>
Signed-off-by: Olof Johansson <olof@lixom.net>