net: mvneta: Convert to use PHY_FIXED for fixed-link

Stop parsing fixed-link in the MAC driver. Instead support only PHY mode
and let the fixed PHY driver handle the fixed-link case.

Enable CONFIG_PHY_FIXED for mvneta boards that need it: Turris Omnia and
ESPRESSObin.

Signed-off-by: Marek BehĂșn <marek.behun@nic.cz>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/configs/turris_omnia_defconfig b/configs/turris_omnia_defconfig
index 5e4f094..217e260 100644
--- a/configs/turris_omnia_defconfig
+++ b/configs/turris_omnia_defconfig
@@ -82,6 +82,7 @@
 CONFIG_SPI_FLASH_SPANSION=y
 CONFIG_SPI_FLASH_MTD=y
 CONFIG_PHY_MARVELL=y
+CONFIG_PHY_FIXED=y
 CONFIG_PHY_GIGE=y
 CONFIG_MVNETA=y
 CONFIG_MII=y