dt-bindings: reset: add sama7g5 definitions

Add reset bindings for SAMA7G5. At the moment only USB PHYs are
included.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>