Merge tag 'u-boot-amlogic-20210406' of https://source.denx.de/u-boot/custodians/u-boot-amlogic

- Add MMIO MDIO mux driver
- Add Amlogic G12A MDIO mux driver
- Add DM_MDIO support for designware ethernet driver
- Add Amlogic Meson8b and later designware ethernet glue driver
- Switch all amlogic boards to Amlogic designware ethernet glue driver
- Switch all amlogic boards to DM_MDIO when necessary
- Remove all static ethernet setup code