x86: chromebox_panther: Convert to use driver model ethernet

This board uses RTL8169 which is a driver model ethernet driver.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

configs/chromebox_panther_defconfig

@@ -25,6 +25,7 @@ CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_GIGADEVICE=y
 CONFIG_SPI_FLASH_MACRONIX=y
 CONFIG_SPI_FLASH_WINBOND=y
+CONFIG_DM_ETH=y
 CONFIG_DM_PCI=y
 CONFIG_DM_RTC=y
 CONFIG_SYS_NS16550=y