phy: sun4i-usb: Support VBUS detection via power supply

The device tree binding provides for getting VBUS state from a device
referenced by phandle, as an optional alternative to using a GPIO. In
U-Boot, where there is no power supply class, this VBUS detection will
be implemented using a regulator device and its get_enable method.
Let's hook this up to the PHY driver.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Acked-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/drivers/phy/allwinner/Kconfig b/drivers/phy/allwinner/Kconfig
index 6bfb79c..d3ff82f 100644
--- a/drivers/phy/allwinner/Kconfig
+++ b/drivers/phy/allwinner/Kconfig
@@ -4,6 +4,7 @@
 config PHY_SUN4I_USB
 	bool "Allwinner Sun4I USB PHY driver"
 	depends on ARCH_SUNXI
+	select DM_REGULATOR
 	select PHY
 	help
 	  Enable this to support the transceiver that is part of Allwinner