In preparation for support of MDIO on AN7581, move the MT7531 MMIO logic
to a dedicated driver and permit usage of the mdio read/write function
to the mtk_eth driver.

This only affect MT7988 that can use MMIO operation to access the Switch
register. The MT7988 code is updated to make use of the external driver.

This permits Airoha driver to make use of DM_MDIO to bind for the MT7531
driver that have the same exact register.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>

In this case, the mediatek network drivers cannot build outside of
ARCH_MEDIATEK or ARCH_MTMIPS, and so express this requirement in Kconfig
as well. In the case of DWC_ETH_XGMAC / DWC_ETH_XGMAC_SOCFPGA, the file
controlled by the DWC_ETH_XGMAC option references a socfpga-specific
array defined in the file controlled by DWC_ETH_XGMAC_SOCFPGA. Rework
these options in Kconfig to handle this dependency.

Signed-off-by: Tom Rini <trini@konsulko.com>

Airoha AN8855 is a 5-port gigabit switch with a 2.5G HSGMII CPU port

Signed-off-by: Weijie Gao <weijie.gao@mediatek.com>

This patch adds support for MediaTek MT7987.

MT7987 features MediaTek NETSYS v3, similar to MT7988, features three GMACs
which support 2.5Gb HSGMII. One 2.5Gb PHY is also embedded an can be
connected to a dedicated GMAC.

Signed-off-by: Weijie Gao <weijie.gao@mediatek.com>

mtk_eth.c contains not only the ethernet GMAC/DMA driver, but also
some ethernet switch initialization code. As we may add more switch
support in the future, it's better to move them out of mtk_eth.c to
avoid increasing the code complexity.

Since not all switches are supported for a particular board, Kconfig
options are added to allow user to select which switch should be
built into u-boot. If multiple switches are selected, auto-detecting
can also be enabled.

Signed-off-by: Weijie Gao <weijie.gao@mediatek.com>