pinctrl: imx: Kconfig: PINCTRL_IMX select REGMAP

Regmap functionality has been integrated into pinctrl-imx.c with commit
8626ada8 which might trigger build failures when regmap is not selected
otherwise. Hence, make Kconfig aware about this new dependency.

Signed-off-by: Alexander Kurz <akurz@blala.de>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>