Add support for RXAUI mode by adding an entry in the COMPHY modes list.

There is no user for this mode yet so we can enforce an up-to-date
firmware and return an error otherwise without breaking anywone.
Signed-off-by: Grzegorz Jaszczyk <jaz@semihalf.com>
[miquel.raynal@bootlin.com: adapt the content to the mainline driver]
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>