enetc: update TSN Qbv PSPEED set according to adjust link speed

ENETC has a register PSPEED to indicate the link speed of hardware.
It is need to update accordingly. PSPEED field needs to be updated
with the port speed for QBV scheduling purposes. Or else there is
chance for gate slot not free by frame taking the MAC if PSPEED and
phy speed not match. So update PSPEED when link adjust. This is
implement by the adjust_link.

Signed-off-by: Po Liu <Po.Liu@nxp.com>
Signed-off-by: Claudiu Manoil <claudiu.manoil@nxp.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>