Merge branch 'follow-up-to-rgmii-mode-clarification-am65-cpsw-fix-checkpatch'

Matthias Schiffer says:

====================
Follow-up to RGMII mode clarification: am65-cpsw fix + checkpatch

Following previous discussion [1] and the documentation update by
Andrew [2]:

Fix up the mode to account for the fixed TX delay on the AM65 CPSW
Ethernet controllers, similar to the way the icssg-prueth does it. For
backwards compatibility, the "impossible" modes that claim to have a
delay on the PCB are still accepted, but trigger a warning message.

As Andrew suggested, I have also added a checkpatch check that requires
a comment for any RGMII mode that is not "rgmii-id".

No Device Trees are updated to avoid the warning for now, to give other
projects syncing the Linux Device Trees some time to fix their drivers
as well. I intend to submit an equivalent change for U-Boot's
am65-cpsw-nuss driver as soon as the changes are accepted for Linux.

[1] https://lore.kernel.org/lkml/d25b1447-c28b-4998-b238-92672434dc28@lunn.ch/
[2] https://lore.kernel.org/all/20250430-v6-15-rc3-net-rgmii-delays-v2-1-099ae651d5e5@lunn.ch/
    commit c360eb0c3ccb ("dt-bindings: net: ethernet-controller: Add informative text about RGMII delays")
v1: https://lore.kernel.org/all/cover.1744710099.git.matthias.schiffer@ew.tq-group.com/
====================

Link: https://patch.msgid.link/cover.1750756583.git.matthias.schiffer@ew.tq-group.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>