net: pcs: lynx: make lynx_pcs_create() static

commit  b043d182c47d9e30f56efcc3e5ebffcbc7284f99 from
https://github.com/nxp-imx/linux-imx lf-6.1.y

We no longer need to export lynx_pcs_create() for drivers to use as we
now have all the functionality we need in the two new creation helpers.
Remove the export and prototype, and make it static.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
(cherry picked from commit 84e476b8

)
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Xiaolei Wang <xiaolei.wang@windriver.com>