usb: phy: hsusb: voltage enablement based on cable connection

This change adds the required flag to guarantee that
HS PHY regulators will only be turned off if the USB
cable is disconnected.

Change-Id: Icfe4b88b2bd522806eed5c19ed62a9846e92aa0f
Signed-off-by: Bar Weiner <bweiner@codeaurora.org>