usb: tegra: Use regulators instead of GPIOs for USB PHY VBUS

The tegra ehci driver has enabled USB vbus regulators directly using
GPIOs and the device tree attribute nvidia,vbus-gpio. This is ugly
and causes error messages on boot when both the regulator driver
and the ehci driver want access to the same GPIO.

After this patch, usb vbus regulators for tegra usb phy devices are specified
with the device tree attribute vbus-supply = <&x> where x is a regulator defined
in the device tree. The old nvidia,vbus-gpio property is no longer supported.

Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>