configs: imx8mm_venice_defconfig: add support for gbe switch

The imx8mm-venice-gw7901 board has an I2C connected KSZ9897S GbE switch
with an IMX8MM FEC MAC master connected via RGMII_ID.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
diff --git a/configs/imx8mm_venice_defconfig b/configs/imx8mm_venice_defconfig
index 3961db0..49affcc 100644
--- a/configs/imx8mm_venice_defconfig
+++ b/configs/imx8mm_venice_defconfig
@@ -87,9 +87,13 @@
 CONFIG_FSL_USDHC=y
 CONFIG_PHYLIB=y
 CONFIG_PHY_TI_DP83867=y
+CONFIG_PHY_FIXED=y
 CONFIG_DM_ETH=y
+CONFIG_DM_MDIO=y
+CONFIG_DM_DSA=y
 CONFIG_PHY_GIGE=y
 CONFIG_FEC_MXC=y
+CONFIG_KSZ9477=y
 CONFIG_MII=y
 CONFIG_PINCTRL=y
 CONFIG_SPL_PINCTRL=y