usb: dwc3: Add DWC_usb31 GRXTHRCFG bit fields

usb: dwc3: Add DWC_usb31 GRXTHRCFG bit fields

Add new GRXTHRCFG bit field macros for DWC_usb31. The GRXTHRCFG register
fields for DWC_usb31 is as follows:
 +-------+--------------------------+----------------------------------+
 | BITS  | Name                     | Description                      |
 +=======+==========================+==================================+
 | 31:27 | reserved                 |                                  |
 | 26    | UsbRxPktCntSel           | Async ESS receive packet         |
 |       |                          | threshold enable                 |
 | 25:21 | UsbRxPktCnt              | Async ESS receive packet         |
 |       |                          | threshold count                  |
 | 20:16 | UsbMaxRxBurstSize        | Async ESS Max receive burst size |
 | 15    | UsbRxThrNumPktSel_HS_Prd | HS high bandwidth periodic       |
 |       |                          | receive packet threshold enable  |
 | 14:13 | UsbRxThrNumPkt_HS_Prd    | HS high bandwidth periodic       |
 |       |                          | receive packet threshold count   |
 | 12:11 | reserved                 |                                  |
 | 10    | UsbRxThrNumPktSel_Prd    | Periodic ESS receive packet      |
 |       |                          | threshold enable                 |
 | 9:5   | UsbRxThrNumPkt_Prd       | Periodic ESS receive packet      |
 |       |                          | threshold count                  |
 | 4:0   | UsbMaxRxBurstSize_Prd    | Max periodic ESS RX burst size   |
 +-------+--------------------------+----------------------------------+

Signed-off-by: Thinh Nguyen <thinhn@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>