Kconfig: gadget: Move CONFIG_USB_FUNCTION_THOR to Kconfig

This commit moves USB_FUNCTION_THOR config to Kconfig.

Signed-off-by: Lukasz Majewski <lukma@denx.de>
Acked-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
diff --git a/configs/xilinx_zynqmp_ep_defconfig b/configs/xilinx_zynqmp_ep_defconfig
index ce8bc0b..7f8e774 100644
--- a/configs/xilinx_zynqmp_ep_defconfig
+++ b/configs/xilinx_zynqmp_ep_defconfig
@@ -95,5 +95,6 @@
 CONFIG_USB_GADGET_MANUFACTURER="Xilinx"
 CONFIG_USB_GADGET_VENDOR_NUM=0x03fd
 CONFIG_USB_GADGET_PRODUCT_NUM=0x0300
+CONFIG_USB_FUNCTION_THOR=y
 # CONFIG_REGEX is not set
 CONFIG_EFI_LOADER_BOUNCE_BUFFER=y