serial: sh: Add RZ/G2L SCIF support

Extend the existing driver to support the SCIF serial ports on the
Renesas RZ/G2L (R9A07G044) SoC. This also requires us to ensure that if
there is a reset signal defined in the device tree, it is de-asserted
before we try to talk to the SCIF module.

Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Tested-by: Marek Vasut <marek.vasut+renesas@mailbox.org> # R-Car H3 Salvator-XS