generic: mt7530: backport support for the MT7988 built-in switch

generic: mt7530: backport support for the MT7988 built-in switch

Backport commits adding support for the MT7988 built-in switch to the
mt7530 driver.

This change results in the Kconfig symbol NET_DSA_MT7530 to be extended
by NET_DSA_MT7530_MDIO (everything formally covered by NET_DSA_MT7530)
and NET_DSA_MT7530_MMIO (a new driver for the MMIO-connected built-in
switch of the MT7988 SoC).

Select NET_DSA_MT7530_MDIO for all targets previously selecting
NET_DSA_MT7530, with the exception of mediatek/filogic which also
selects NET_DSA_MT7530_MMIO.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
(cherry picked from commit 958fdf36e35c814eb83faf2c39db4ca379c921b5)