net: phy: Replace PHY_ANEG_TIMEOUT with Kconfig symbol

Switch PHY_ANEG_TIMEOUT to CONFIG_PHY_ANEG_TIMEOUT Kconfig symbol.
This removes one more configuration headers option finalizes its
Kconfig symbol conversion. No functional change expected.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
diff --git a/configs/imx8mp_beacon_defconfig b/configs/imx8mp_beacon_defconfig
index b0dcbc7..3c337d4 100644
--- a/configs/imx8mp_beacon_defconfig
+++ b/configs/imx8mp_beacon_defconfig
@@ -113,6 +113,7 @@
 CONFIG_SPI_FLASH_ATMEL=y
 CONFIG_SPI_FLASH_STMICRO=y
 CONFIG_SPI_FLASH_MTD=y
+CONFIG_PHY_ANEG_TIMEOUT=20000
 CONFIG_PHY_MICREL=y
 CONFIG_PHY_MICREL_KSZ90X1=y
 CONFIG_DM_ETH_PHY=y