ath79: generic: add support for Realtek PHY

Some models of the TP-Link EAP225 series use a Realtek PHY,
therefore the driver is added.

Signed-off-by: Philipp Rothmann <philipprothmann@posteo.de>

target/linux/ath79/generic/config-default

@@ -18,6 +18,7 @@ CONFIG_MTD_REDBOOT_PARTS=y
 CONFIG_MTD_SPLIT_EVA_FW=y
 CONFIG_PHY_AR7100_USB=y
 CONFIG_PHY_AR7200_USB=y
+CONFIG_REALTEK_PHY=y
 CONFIG_REGULATOR_FIXED_VOLTAGE=y
 CONFIG_RTL8366RB_PHY=y
 CONFIG_RTL8366S_PHY=y