pinctrl: renesas: rzn1: Enable missing PINMUX

Enable pin muxing (eg. programmable function), so that the RZ/N1 GPIO
pins will be configured as specified by the pinmux in the DTS.

This used to be enabled implicitly via CONFIG_GENERIC_PINMUX_FUNCTIONS,
however that was removed, since the RZ/N1 driver does not call any of
the generic pinmux functions.

Fixes: 1308fb4e

 ("pinctrl: rzn1: Do not select GENERIC_PIN{CTRL_GROUPS,MUX_FUNCTIONS}")
Signed-off-by: Ralph Siemsen <ralph.siemsen@linaro.org>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20231004200008.1306798-1-ralph.siemsen@linaro.org
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>