ARM: shmobile: r8a7790 IRQC support

Add IRQC interrupt controller support to r8a7790 by
hooking up a single IRQC instances to handle 4 external
IRQ signals. The IRQC controller is tied to SPIs of
the GIC. On r8a7790 the external IRQ pins routing is
handled by the PFC which is excluded from this patch.

Both platform devices and DT devices are added in this
patch. The platform device versions are used to provide
a static interrupt map configuration for board code
written in C.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>