net: phylink: add support for PCS supported_interfaces bitmap

Add support for the PCS to specify which interfaces it supports, which
can be used by MAC drivers to build the main supported_interfaces
bitmap. Phylink also validates that the PCS returned by the MAC driver
supports the interface that the MAC was asked for.

An empty supported_interfaces bitmap from the PCS indicates that it
does not provide this information, and we handle that appropriately.

Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1tTffL-007RoD-1Y@rmk-PC.armlinux.org.uk


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