dt-bindings: ethernet-phy: add optional brr-mode flag

There is a group of PHY chips supporting BroadR-Reach link modes in
a manner allowing for more or less identical register usage as standard
Clause 22 PHY.
These chips support standard Ethernet link modes as well, however, the
circuitry is mutually exclusive and cannot be auto-detected.
The link modes in question are 100Base-T1 as defined in IEEE802.3bw,
based on Broadcom's 1BR-100 link mode, and newly defined 10Base-T1BRR
(1BR-10 in Broadcom documents).

Add optional brr-mode flag to switch the PHY to BroadR-Reach mode.

Signed-off-by: Kamil Horák (2N) <kamilh@axis.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://patch.msgid.link/20240712150709.3134474-4-kamilh@axis.com


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