phy: lynx-28g: move lane mode helpers to new core module

phy: lynx-28g: move lane mode helpers to new core module

Do some preparation work for the introduction of the lynx-10g driver,
which will share a common backbone with the 28G Lynx SerDes.

This is just trivial stuff which can be moved without any surgery, and
is easy to follow but otherwise pollutes more serious changes.

The lane modes themselves are exported to a public header, because on
the 10G Lynx, the hardware requires implementing a procedure called
"RCW override". This requires coordination with drivers/soc/fsl/guts.c
to tell it that a SerDes lane needs to be switched to a different
protocol (enum lynx_lane_mode).

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://patch.msgid.link/20260610151952.2141019-4-vladimir.oltean@nxp.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>