ram: renesas: rtvram: Add support for Renesas R-Car Gen5

Add support for Renesas R-Car Gen5 R8A78000 SoC into RT-VRAM
initialization driver. The changes are only a slight adjustment
to the register programming, therefore reuse the existing RT-VRAM
driver and parametrize those changes using driver data.

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