net: remove explicit phylink_generic_validate() references

Virtually all conventional network drivers are now converted to use
phylink_generic_validate() - only DSA drivers and fman_memac remain,
so lets remove the necessity for network drivers to explicitly set
this member, and default to phylink_generic_validate() when unset.
This is possible as .validate must currently be set.

Any remaining instances that have not been addressed by this patch can
be fixed up later.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/E1or0FZ-001tRa-DI@rmk-PC.armlinux.org.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>