ramips: mt7620: move mt7620_mdio_mode() to ethernet driver

ramips: mt7620: move mt7620_mdio_mode() to ethernet driver

The function mt7620_mdio_mode is only called once
and both the function and mdio_mode block have been named incorrectly,
leading to confusion and useless commits.

These lines in the mdio_mode block of mt7620_hw_init
are only intended for boards with an external mt7530 switch.
(see commit 194ca6127ee18cd3a95da4d03f02e43b5428c0bb)

Therefore, move lines from mdio_mode to the place in soc_mt7620.c
where the type of mt7530 switch is identified,
and move lines from mt7620_mdio_mode to a main function.

mt7620_mdio_mode was called from mt7620_gsw_init
where the priv struct is available,
so the lines must stay in mt7620_gsw_init function.

In order to keep things as simple as possible,
keep the DTS property related function calls together,
by moving them from mt7620_gsw_probe to init.

Remove the now useless DTS properties and extra phy nodes.

Fixes: 5a6229a93df8 ("ramips: remove superfluous & confusing DT binding")
Fixes: b85fe43ec8c4 ("ramips: mt7620: add force use of mdio-mode")
Signed-off-by: Michael Pratt <mcpratt@pm.me>
(cherry picked from commit 6972e498d33ec896c676b7af91e3bfb00aa846a1)