mvebu: usb: xhci: Add VBUS regulator supply to the host driver

mvebu: usb: xhci: Add VBUS regulator supply to the host driver

The USB device should linked to VBUS regulator through "vbus-supply"
DTS property.
This patch adds handling for "vbus-supply" property inside the USB
device entry for turning on the VBUS regulator upon the host adapter probe.

Signed-off-by: Konstantin Porotchkin <[email protected]>
Cc: Stefan Roese <[email protected]>
Cc: Marek Vasut <[email protected]>
Cc: Nadav Haklai <[email protected]>
Cc: Neta Zur Hershkovits <[email protected]>
Cc: Igal Liberman <[email protected]>
Cc: Haim Boot <[email protected]>
Acked-by: Marek Vasut <[email protected]>
Signed-off-by: Stefan Roese <[email protected]>