net: pcs: xpcs: get rid of xpcs_init_iface()

xpcs_init_iface() no longer does anything with the interface mode, and
now merely does configuration related to the PMA ID. Move this back
into xpcs_create() as it doesn't warrant being a separate function
anymore.

Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1svfML-005ZIF-84@rmk-PC.armlinux.org.uk


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