mmc: renesas-sdhi: Initialize module on RZ/G2L

On the Renesas RZ/G2L SoC family, we must ensure that the required clock
signals are enabled and the reset signal is de-asserted before we try to
communicate with the SDHI 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>