phy: tegra: Select USB_PHY

phy: tegra: Select USB_PHY

I have hit the following build error:

	armv7a-hardfloat-linux-gnueabi-ld: drivers/phy/tegra/xusb.o: in function `tegra_xusb_port_unregister':
	xusb.c:(.text+0x2ac): undefined reference to `usb_remove_phy'
	armv7a-hardfloat-linux-gnueabi-ld: drivers/phy/tegra/xusb.o: in function `tegra_xusb_setup_ports':
	xusb.c:(.text+0xf30): undefined reference to `usb_add_phy_dev'

PHY_TEGRA_XUSB should select USB_PHY because it uses symbols defined in
the code enabled by that.

Fixes: 23babe30fb45d ("phy: tegra: xusb: Add usb-phy support")
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>