usb: move phy driver from mach-tegra to drivers/usb

As part of this patch:
	1. Moved existing tegra phy driver to drivers/USB directory.
	2. Added standard USB phy driver APIs to tegra phy driver.

Signed-off-by: Venu Byravarasu <vbyravarasu@nvidia.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>