arm64: dts: r8a7795: Link ARM GIC to clock and clock domain

Link the ARM GIC to the INTC-AP module clock, and add it to the SYSC
"always-on" PM Domain, so it can be power managed using that clock.

Note that currently the GIC-400 driver doesn't support module clocks nor
Runtime PM, so this must be handled as a critical clock.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>