ARM: dts: renesas: Replace R8A77950 with R8A77951

R-Car R8A77950 H3 ES1.* was only available to an internal development
group and needed a lot of quirks and workarounds. Public users only
have R-Car R8A77950 H3 ES2 and newer. Switch existing systems to use
R8A77951 device trees.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>