clk: renesas: rcar-gen4: Introduce R-Car Gen4 CPG driver

According to the official website [1], the R-Car V3U SoC is based
on the R-Car Gen4 architecture. So, introduce R-Car Gen4 CPG
driver.

[1]
https://www.renesas.com/us/en/products/automotive-products/automotive-system-chips-socs/r-car-v3u-best-class-r-car-v3u-asil-d-system-chip-automated-driving



Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/20211201073308.1003945-9-yoshihiro.shimoda.uh@renesas.com


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