arm64: dts: marvell: armada-7040-db: Add USB current regulators

Armada 7040-db USB ports deliver 500mA by default while they
could deliver up to 900mA (usually, for USB3 devices).

The board embeds a GPIO controlled regulator on each port which can be
configured to deliver each amount of current.

Add a vin-supply property to the USB3 Vbus nodes for this purpose. The
regulator will be automatically 'enabled', ie. set to limit at 900mA
instead of 500mA.

Suggested-by: Alex Leibovich <alexl@marvell.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>