usb: dwc3: Update DWC_usb31 GTXFIFOSIZ reg fields

Update two GTXFIFOSIZ bit fields for the DWC_usb31 controller. TXFDEP
is a 15-bit value instead of 16-bit value, and bit 15 is TXFRAMNUM.

The GTXFIFOSIZ register for DWC_usb31 is as follows:
 +-------+-----------+----------------------------------+
 | BITS  | Name      | Description                      |
 +=======+===========+==================================+
 | 31:16 | TXFSTADDR | Transmit FIFOn RAM Start Address |
 | 15    | TXFRAMNUM | Asynchronous/Periodic TXFIFO     |
 | 14:0  | TXFDEP    | TXFIFO Depth                     |
 +-------+-----------+----------------------------------+

Change-Id: I3179236b9044e27bcc929f5b55d326a4686b9c40
Signed-off-by: Thinh Nguyen <thinhn@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Patch-mainline: linux-usb @ 01/31/18, 13:15
Signed-off-by: Mayank Rana <mrana@codeaurora.org>