net: pcs: xpcs: fill in PCS supported_interfaces

Fill in the new PCS supported_interfaces member with the interfaces
that XPCS supports.

Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1tTffQ-007RoJ-4u@rmk-PC.armlinux.org.uk


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