arm64: dts: renesas: r8a77990: Revise the psci node

The basic support patch 9491a8b17530 ("arm64: dts: renesas: Add Renesas
R8A77990 SoC support") lacks the compatible "arm,psci-1.0" in the psci
node. So, this patch revises it.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>