MAINTAINERS: Add DT Bindings for Renesas Pin Function Controllers

The "PIN CONTROLLER - RENESAS" section lacks the related DT bindings.
Add them.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/20200417141003.22816-1-geert+renesas@glider.be

MAINTAINERS

@@ -13346,6 +13346,7 @@ M:	Geert Uytterhoeven <geert+renesas@glider.be>
 L:	linux-renesas-soc@vger.kernel.org
 S:	Maintained
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/geert/renesas-drivers.git sh-pfc
+F:	Documentation/devicetree/bindings/pinctrl/renesas,*
 F:	drivers/pinctrl/pinctrl-rz*
 F:	drivers/pinctrl/sh-pfc/