amd-xgbe: add support for new XPCS routines

amd-xgbe: add support for new XPCS routines

Add the necessary support to enable Renoir ethernet device. Since the
BAR1 address cannot be used to access the XPCS registers on Renoir, use
the smn functions.

Some of the ethernet add-in-cards have dual PHY but share a single MDIO
line (between the ports). In such cases, link inconsistencies are
noticed during the heavy traffic and during reboot stress tests. Using
smn calls helps avoid such race conditions.

Suggested-by: Sudheesh Mavila <sudheesh.mavila@amd.com>
Signed-off-by: Raju Rangoju <Raju.Rangoju@amd.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250509155325.720499-4-Raju.Rangoju@amd.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>