net: phy: phy_caps: Allow looking-up link caps based on speed and duplex

net: phy: phy_caps: Allow looking-up link caps based on speed and duplex

As the link_caps array is efficient for <speed,duplex> lookups,
implement a function for speed/duplex lookups that matches a given
mask. This replicates to some extent the phy_lookup_settings()
behaviour, matching full link_capabilities instead of a single linkmode.

phy.c's phy_santize_settings() and phylink's
phylink_ethtool_ksettings_set() performs such lookup using the
phy_settings table, but are only interested in the actual speed/duplex
that were matched, rathet than the individual linkmode.

Similar to phy_lookup_settings(), the newly introduced phy_caps_lookup()
will run through the link_caps[] array by descending speed/duplex order.

If the link_capabilities for a given <speed/duplex> tuple intersects the
passed linkmodes, we consider that a match.

Similar to phy_lookup_settings(), we also allow passing an 'exact'
boolean, allowing non-exact match. Here, we MUST always match the
linkmodes mask, but we allow matching on lower speed settings.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/20250307173611.129125-8-maxime.chevallier@bootlin.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>