net: macb: convert to phylink

This patch converts the MACB Ethernet driver to the Phylink framework.
The MAC configuration is moved to the Phylink ops and Phylink helpers
are now used in the ethtools functions. This helps to access the flow
control and pauseparam logic and this will be helpful in the future for
boards using this controller with SFP cages.

Tested-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>