arm64: dts: renesas: r8a77990: Add GPIO device nodes

This patch adds GPIO nodes for r8a77990 (R-Car E3).

Based on a patch from Takeshi Kihara <takeshi.kihara.df@renesas.com>

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
[simon: dropped use of deprecated "renesas,gpio-rcar"]
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>