phy: phy-imx8mq-usb: add vbus regulator support

Add support for enabling and disabling vbus-supply regulator found
on several imx8mp boards in the usb3_phy0 and usb3_phy1 nodes.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Reviewed-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>