ARM: dts: sama7g5: Add USB and UTMI DT nodes

Define the USB and UTMI DT nodes for the sama7g5 SoC's. 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>
Reviewed-by: Marek Vasut <marex@denx.de>