pinctrl: renesas: r8a7791: Optimize pinctrl image size for R8A774[34]

This driver supports both RZ/G1[MN] and R-Car M2-W/M2-N SoCs.
Optimize pinctrl image size for RZ/G1[MN], when support for R-Car
M2-W/M2-N (R8A779[13]) is not enabled.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://lore.kernel.org/r/20201019124258.4574-7-biju.das.jz@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>