net: phy: mxl-gpy: print firmware in human readable form

Now having a major and a minor number, also print the firmware in
human readable form "major.minor". Still keep the 4-digit hexadecimal
representation because that form is used in the firmware changelog
documents. Also, drop the "release" string assuming that most common
case, but make it clearer that the user is running a test version.

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>