net: phy: meson-gxl: leave CONFIG_A6 untouched

The PHY performs just as well when left in its default configuration and
it makes senses because this poke gets reset just after init.

According to the documentation, all registers in the Analog/DSP bank are
reset when there is a mode switch from 10BT to 100BT. The bank is also
reset on power down and soft reset, so we will never see the value which
may have been set by the bootloader.

In the end, we have used the default configuration so far and there is no
reason to change now. Remove CONFIG_A6 poke to make this clear.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: David S. Miller <davem@davemloft.net>