arm64: dts: armada-3720-turris-mox: convert usb-phy to phy-supply

Update Turris Mox device tree to use the phy-supply property of the
generic PHY framework instead of the legacy usb-phy property.

This is needed since it caused a regression on Turris Mox since "usb:
host: xhci-plat: Prevent an abnormally restrictive PHY init skipping".

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Fixes: eb6c2eb6 ("usb: host: xhci-plat: Prevent an abnormally restrictive PHY init skipping")
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>