phy: marvell: cp110: let the firmware perform training for XFI

Replace the XFI training with appropriate SMC call, so the firmware will
perform exact initialization.

Update Stefan 2021-03-23:
Move comphy_smc() function to an earlier place - necessary for the
mainline merge.

Change-Id: I789b130b05529dc80dadcf66aef407d93595b762
Signed-off-by: Grzegorz Jaszczyk <jaz@semihalf.com>
Signed-off-by: Stefan Roese <sr@denx.de>
Reviewed-by: Igal Liberman <igall@marvell.com>