rockchip: firefly-rk3399: enable CONFIG_USB_DWC3

To fix below build error:
drivers/usb/host/built-in.o: In function `xhci_dwc3_remove':
drivers/usb/host/xhci-dwc3.c:174: undefined reference to `dwc3_shutdown_phy'
drivers/usb/host/built-in.o: In function `xhci_dwc3_probe':
drivers/usb/host/xhci-dwc3.c:130: undefined reference to `dwc3_setup_phy'
Signed-off-by: NKever Yang <kever.yang@rock-chips.com>

configs/firefly-rk3399_defconfig

@@ -8,6 +8,7 @@ CONFIG_NR_DRAM_BANKS=1
 CONFIG_DEBUG_UART_BASE=0xFF1A0000
 CONFIG_DEBUG_UART_CLOCK=24000000
 CONFIG_DEBUG_UART=y
+CONFIG_DEFAULT_DEVICE_TREE="rk3399-firefly"
 CONFIG_DEFAULT_FDT_FILE="rockchip/rk3399-firefly.dtb"
 CONFIG_MISC_INIT_R=y
 CONFIG_DISPLAY_BOARDINFO_LATE=y
@@ -23,7 +24,6 @@ CONFIG_CMD_USB=y
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_CMD_TIME=y
 CONFIG_SPL_OF_CONTROL=y
-CONFIG_DEFAULT_DEVICE_TREE="rk3399-firefly"
 CONFIG_OF_SPL_REMOVE_PROPS="pinctrl-0 pinctrl-names clock-names interrupt-parent assigned-clocks assigned-clock-rates assigned-clock-parents"
 CONFIG_ENV_IS_IN_MMC=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
@@ -54,6 +54,8 @@ CONFIG_USB_XHCI_HCD=y
 CONFIG_USB_XHCI_DWC3=y
 CONFIG_USB_EHCI_HCD=y
 CONFIG_USB_EHCI_GENERIC=y
+CONFIG_USB_DWC3=y
+CONFIG_USB_DWC3_GENERIC=y
 CONFIG_USB_HOST_ETHER=y
 CONFIG_USB_ETHER_ASIX=y
 CONFIG_USB_ETHER_ASIX88179=y