phy-sun4i-usb: Add support for monitoring vbus via a power-supply

On some boards there is no vbus_det gpio pin, instead vbus-detection for
otg can be done via the pmic.

This commit adds support for monitoring vbus_det via the power_supply
exported by the pmic, enabling support for otg on these boards.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
diff --git a/drivers/phy/Kconfig b/drivers/phy/Kconfig
index c0c1ad2..0fe9bff 100644
--- a/drivers/phy/Kconfig
+++ b/drivers/phy/Kconfig
@@ -209,6 +209,7 @@
 	depends on ARCH_SUNXI && HAS_IOMEM && OF
 	depends on RESET_CONTROLLER
 	depends on EXTCON
+	depends on POWER_SUPPLY
 	select GENERIC_PHY
 	help
 	  Enable this to support the transceiver that is part of Allwinner