enetc: Remove the imdio bus on PF probe bailout

enetc_imdio_remove() is missing from the enetc_pf_probe()
bailout path. Not surprisingly because enetc_setup_serdes()
is registering the imdio bus for internal purposes, and it's
not obvious that enetc_imdio_remove() currently performs the
teardown of enetc_setup_serdes().
To fix this, define enetc_teardown_serdes() to wrap
enetc_imdio_remove() (improve code maintenance) and call it
on bailout and remove paths.

Fixes: 975d183e

 ("net: enetc: Initialize SerDes for SGMII and USXGMII protocols")
Signed-off-by: Claudiu Manoil <claudiu.manoil@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>