net: phylink: add phylink_get_link_timer_ns() helper

commit  cc8ee2386adbe9fb599b37594f7af2e62ef0d1f8 from
https://github.com/nxp-imx/linux-imx

 lf-6.1.y

Add a helper to convert the PHY interface mode to the required link
timer setting as stated by the appropriate standard. Inappropriate
interface modes return an error.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
(cherry picked from commit 9c5a1706)
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Xiaolei Wang <xiaolei.wang@windriver.com>