arm64: dts: renesas: r8a77980: add SMP support

Add the device nodes for 3 more Cortex-A53 CPU cores; adjust the interrupt
delivery masks for the ARM GIC and Architectured Timer.

Based on the original (and large) patch by Vladimir Barinov.

Signed-off-by: Vladimir Barinov <vladimir.barinov@cogentembedded.com>
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
[simon: corrected whitespace]
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>