net: phy: phy_caps: Move phy_speeds to phy_caps

Use the newly introduced link_capabilities array to derive the list of
possible speeds when given a combination of linkmodes. As
link_capabilities is indexed by speed, we don't have to iterate the
whole phy_settings array.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/20250307173611.129125-4-maxime.chevallier@bootlin.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>