usb: dwc3: add P3 in U2 SS inactive quirk

This patch adds P3 in U2 SS inactive quirk, and some special platforms can
configure that if it is needed.

[ balbi@ti.com : added DeviceTree binding documentation ]

Signed-off-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>