This patch allows the dwc3 driver to run on the new Synopsys USB 3.1
IP core, albeit in USB 3.0 mode only.

The Synopsys USB 3.1 IP (DWC_usb31) retains mostly the same register
interface and programming model as the existing USB 3.0 controller IP
(DWC_usb3). However the GSNPSID and version numbers are different.

Add checking for the new ID to pass driver probe.

Also, since the DWC_usb31 version number is lower in value than the
full GSNPSID of the DWC_usb3 IP, we set the high bit to identify
DWC_usb31 and to ensure the values are higher.

Finally, add a documentation note about the revision numbering scheme.
Any future revision checks (for STARS, workarounds, and new features)
should take into consideration how it applies to both the 3.1/3.0 IP.

Cc: <stable@vger.kernel.org> # v3.18+
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>