pinctrl: renesas: rzg2l: Add suspend/resume support for Schmitt control registers

Renesas RZ/G3E supports a power-saving mode where power to most of the
SoC components is lost, including the PIN controller.  Save and restore
the Schmitt control register contents to ensure the functionality is
preserved after a suspend/resume cycle.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Tested-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com> # on RZ/G3S
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/20250819084022.20512-1-biju.das.jz@bp.renesas.com


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