net: dsa: sja1105: use phylink_pcs internally

Use xpcs_create_pcs_mdiodev() to create the XPCS instance, storing
and using the phylink_pcs pointer internally, rather than dw_xpcs.
Use xpcs_destroy_pcs() to destroy the XPCS instance when we've
finished with it.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1svfMk-005ZIj-R3@rmk-PC.armlinux.org.uk


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