net: pcs: rearrange C73 functions to prepare for C37 support later

commit 5f37d6924be729ef353402477027331f2f9a5065 from
https://source.codeaurora.org/external/autobsps32/linux



The current implementation for XPCS is validated for C73, so we rename them
to have _c73 suffix and introduce a set of functions to use an_mode flag
to switch between C73 and C37 AN later.

Issue: ALB-8243
Signed-off-by: Ong Boon Leong <boon.leong.ong@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 07a4bc51)
Signed-off-by: Radu Pirea (NXP OSS) <radu-nicolae.pirea@oss.nxp.com>
Signed-off-by: Zhantao Tang <zhantao.tang@windriver.com>