net: phy: meson-gxl: clean-up gxl variant driver

The purpose of this change is to align the gxl and g12a driver
declaration.

Like on the g12a variant, remove genphy_aneg_done() from the driver
declaration as the net phy framework will default to it anyway.

Also, the gxl phy id should be an exact match as well, so let's change
this and use the macro provided.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>