dt-bindings: reset: atmel,at91sam9260-reset: add sama7g5 bindings

Add documentation for SAMA7G5 reset controller. Compared with previous
versions of reset controllers this one contains support for resetting
in SoC devices (e.g. USB PHYs).

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>