net: phy: MII-Lite PHY interface mode

net: phy: MII-Lite PHY interface mode

Some Broadcom PHYs are capable to operate in simplified MII mode,
without TXER, RXER, CRS and COL signals as defined for the MII.
The MII-Lite mode can be used on most Ethernet controllers with full
MII interface by just leaving the input signals (RXER, CRS, COL)
inactive. The absence of COL signal makes half-duplex link modes
impossible but does not interfere with BroadR-Reach link modes on
Broadcom PHYs, because they are all full-duplex only.

Add MII-Lite interface mode, especially for Broadcom two-wire PHYs.

Signed-off-by: Kamil Horák - 2N <kamilh@axis.com>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/20250708090140.61355-2-kamilh@axis.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>