Merge branch 'net-phy-QUSGMII'

Maxime Chevallier says:

====================
net: Introduce QUSGMII phy mode

Re-sending, since the previous v4 was sent while net-next was closed.

This is a resend of the V4 of a previous series [1] initially aimed at
introducing inband extensions, with modes like QUSGMII. This mode allows
passing info in the ethernet preamble between the MAC and the PHY, such as
timestamps.

This series has now become a preliminary series, that simply introduces
the new interface mode, without support for inband extensions, that will
come later.

The reasonning is that work will need to be done in the networking
subsystem, but also in the generic phy driver subsystem to allow serdes
configuration for qusgmii.

This series add the mode, the relevant binding changes, adds support for
it in the lan966x driver, and also introduces a small helper to get the
number of links a given phy mode can carry (think 1 for SGMII and 4 for
QSGMII). This allows for better readability and will prove useful
when (if) we support PSGMII (5 links on 1 interface) and OUSGMII (8
links on one interface).

V4 contains no change but the collected Reviewed-by from Andrew.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>