net: fman: fix 2.5G SGMII settings

The settings for 2.5G SGMII are wrong, which the 2.5G case is missed in
set_if_mode(), and the serdes PCS configuration are wrong, this patch uses
the correct settings took from Linux.

Signed-off-by: Shaohui Xie <Shaohui.Xie@nxp.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>