usb: gadget: Move USBNET_HOST_ADDR to Kconfig

While the USB Ethernet device address is already defined in Kconfig, the
host address isn't. Convert it.

Reviewed-by: Ɓukasz Majewski <lukma@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
diff --git a/configs/am335x_evm_norboot_defconfig b/configs/am335x_evm_norboot_defconfig
index c5e7425..c9eab68 100644
--- a/configs/am335x_evm_norboot_defconfig
+++ b/configs/am335x_evm_norboot_defconfig
@@ -35,6 +35,7 @@
 CONFIG_G_DNL_MANUFACTURER="Texas Instruments"
 CONFIG_G_DNL_VENDOR_NUM=0x0451
 CONFIG_G_DNL_PRODUCT_NUM=0xd022
+CONFIG_USBNET_HOST_ADDR="de:ad:be:af:00:00"
 CONFIG_LZO=y
 CONFIG_OF_LIBFDT=y
 CONFIG_OF_LIBFDT_OVERLAY=y