net: phy: mediatek: Change to more meaningful macros

Replace magic number with more meaningful macros in mtk-ge.c.
Also, move some common macros into mtk-phy-lib.c.

Signed-off-by: Sky Huang <skylake.huang@mediatek.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250213080553.921434-2-SkyLake.Huang@mediatek.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>