MAINTAINERS: add pinctrl-apple-gpio to ARM/APPLE MACHINE

Add the Apple SoC pinctrl driver to the ARM/APPLE MACHINE entry
in MAINTAINERS.

Signed-off-by: Joey Gouly <joey.gouly@arm.com>

MAINTAINERS

@@ -1722,6 +1722,7 @@ F:	Documentation/devicetree/bindings/interrupt-controller/apple,aic.yaml
 F:	Documentation/devicetree/bindings/pinctrl/apple,pinctrl.yaml
 F:	arch/arm64/boot/dts/apple/
 F:	drivers/irqchip/irq-apple-aic.c
+F:	drivers/pinctrl/pinctrl-apple-gpio.c
 F:	include/dt-bindings/interrupt-controller/apple-aic.h
 F:	include/dt-bindings/pinctrl/apple.h