net: mscc: ocelot: drop workaround for forcing RX flow control

As phylink gained generic support for PHYs with rate matching via PAUSE
frames, the phylink_mac_link_up() method will be called with the maximum
speed and with rx_pause=true if rate matching is in use. This means that
setups with 2500base-x as the SERDES protocol between the MAC/PCS and
the PHY now work with no need for the driver to do anything special.

Tested with fsl-ls1028a-qds-7777.dts.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>