tty: serial: sh-sci: Add support for R-Car Gen4

Add serial support for R-Car Gen4 SoC.

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/20211209070817.1223888-3-yoshihiro.shimoda.uh@renesas.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>