board: amlogic: enable PHY_REALTEK for selected boards

When using the generic PHY on boards using an RGMII Realtek PHY,
gigabit speed is not always reliable.

This patch enables the Realtek PHY driver for such boards.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
diff --git a/configs/odroid-c2_defconfig b/configs/odroid-c2_defconfig
index 04904c2..66e59e5 100644
--- a/configs/odroid-c2_defconfig
+++ b/configs/odroid-c2_defconfig
@@ -29,6 +29,7 @@
 CONFIG_MMC_MESON_GX=y
 CONFIG_DM_ETH=y
 CONFIG_ETH_DESIGNWARE=y
+CONFIG_PHY_REALTEK=y
 CONFIG_PINCTRL=y
 CONFIG_PINCTRL_MESON_GXBB=y
 CONFIG_DM_REGULATOR=y