ARM: dts: sama7g5ek: Add pinctrl, gpio and phy properties for USB

Add the required pinctrl, gpio and phy properties required by the
USB DT nodes of the sama7g5ek boards. Since these have not yet been
defined in upstream Linux, place them in the U-Boot specific DT file.

Signed-off-by: Sergiu Moga <sergiu.moga@microchip.com>