soc: renesas: rcar-rst: Add support for R-Car S4-8

Add support for R-Car S4-8 (R8A779F0) to the R-Car RST driver.
The register map of R-Car S4-8 is the same as R-Car V3U so that
renames "V3U" and "r8a779a0" to "Gen4".

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/20211201073308.1003945-11-yoshihiro.shimoda.uh@renesas.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>