net: phylink: Convert capabilities to linkmodes using phy_caps

net: phylink: Convert capabilities to linkmodes using phy_caps

phylink_caps_to_linkmodes() is used to derive a list of linkmodes that
can be conceivably exposed using a given set of speeds and duplex
through phylink's MAC capabilities.

This list can be derived from the link_caps array in phy_caps, provided
we convert the MAC capabilities into a LINK_CAPA bitmask first.

Introduce an internal phylink helper phylink_caps_to_link_caps() to
convert from MAC capabilities into phy_caps, then  phy_caps_linkmodes()
to do the link_caps -> linkmodes conversion.

This avoids having to update phylink for every new linkmode.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/20250307173611.129125-13-maxime.chevallier@bootlin.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>