pinctrl: renesas: r8a7796: Optimize pinctrl image size for R8A774A1

This driver supports both RZ/G2M and R-Car M3-W/W+ SoCs.
Optimize pinctrl image size for RZ/G2M, when support for R-Car M3-W/W+
(R8A7796[01]) is not enabled.

Based on the similar patch on Linux.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>