ramips: mt7620: ethernet: use more macros and bump version

ramips: mt7620: ethernet: use more macros and bump version

Define and use some missing macros,
and use them instead of BIT() or numbers for more readable code.

Add comment for a bit change that seems unrelated to ethernet
but is actually needed (PCIe Root Complex mode).

Remove unknown and unused macro RST_CTRL_MCM
(probably from MT7621 / MT7622)

This is the last of a series of fixes, so bump version.

Signed-off-by: Michael Pratt <mcpratt@pm.me>