MAINTAINERS: add documentation file for Microchip SAMA5D2 shutdown controller

Add documentation file for SAMA5D2 shutdown controller.
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

MAINTAINERS

@@ -13856,6 +13856,7 @@ F:	include/dt-bindings/iio/adc/at91-sama5d2_adc.h
 MICROCHIP SAMA5D2-COMPATIBLE SHUTDOWN CONTROLLER
 M:	Claudiu Beznea <claudiu.beznea@microchip.com>
 S:	Supported
+F:	Documentation/devicetree/bindings/power/reset/atmel,sama5d2-shdwc.yaml
 F:	drivers/power/reset/at91-sama5d2_shdwc.c
 
 MICROCHIP SPI DRIVER