net: phy: aquantia: clear PMD Global Transmit Disable bit during init

net: phy: aquantia: clear PMD Global Transmit Disable bit during init

PMD Global Transmit Disable bit should be cleared for normal operation.
This should be HW default, however I found that on Asus RT-AX89X that uses
AQR113C PHY and firmware 5.4 this bit is set by default.

With this bit set the AQR cannot achieve a link with its link-partner and
it took me multiple hours of digging through the vendor GPL source to find
this out, so lets always clear this bit during .config_init() to avoid a
situation like this in the future.

Signed-off-by: Robert Marko <robimarko@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20240211181732.646311-1-robimarko@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>