roc-rk3399-pc: Enable USB3.0 Host

Enable USB3.0 Host support for ROC-RK3399-PC boards.

Tested USB3.0 SSD on Type C1 port on board.

=> usb start
starting USB...
Bus usb@fe380000: USB EHCI 1.00
Bus usb@fe3c0000: USB EHCI 1.00
Bus dwc3: usb maximum-speed not found
Register 2000140 NbrPorts 2
Starting the controller
USB XHCI 1.10
scanning bus usb@fe380000 for devices... 1 USB Device(s) found
scanning bus usb@fe3c0000 for devices... 2 USB Device(s) found
scanning bus dwc3 for devices... 6 USB Device(s) found
       scanning usb for storage devices... 1 Storage Device(s) found
=> usb tree
USB device tree:
  1  Hub (480 Mb/s, 0mA)
     u-boot EHCI Host Controller

  1  Hub (480 Mb/s, 0mA)
  |  u-boot EHCI Host Controller
  |
  +-2  Hub (480 Mb/s, 100mA)
        USB 2.0 Hub [MTT]

  1  Hub (5 Gb/s, 0mA)
  |  U-Boot XHCI Host Controller
  |
  +-2  Hub (480 Mb/s, 0mA)
  | |  VIA Labs, Inc. USB2.0 Hub
  | |
  | +-4  Hub (480 Mb/s, 100mA)
  |   |   USB 2.0 Hub
  |   |
  |   +-5   (480 Mb/s, 100mA)
  |        VIA Technologies Inc. USB 2.0 BILLBOARD  0000000000000001
  |
  +-3  Hub (5 Gb/s, 0mA)
    |  VIA Labs, Inc. USB3.0 Hub
    |
    +-6  Mass Storage (5 Gb/s, 224mA)
         JMicron External Disk 3.0 DB12345678A2

=> usb reset
resetting USB...
Bus usb@fe380000: USB EHCI 1.00
Bus usb@fe3c0000: USB EHCI 1.00
Bus dwc3: usb maximum-speed not found
Register 2000140 NbrPorts 2
Starting the controller
USB XHCI 1.10
scanning bus usb@fe380000 for devices... 1 USB Device(s) found
scanning bus usb@fe3c0000 for devices... 2 USB Device(s) found
scanning bus dwc3 for devices... 6 USB Device(s) found
       scanning usb for storage devices... 1 Storage Device(s) found

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>