ath79: use "fixed-layout" for Embedded Wireless devices

ath79: use "fixed-layout" for Embedded Wireless devices

Those devices have Ethernet interfaces using base MAC address increased
by 0x40 in the 3rd indexed byte (00:00:00:FF:00:00). To describe that we
were using a custom (downstream) "mac-address-increment-byte" property.

The same result can be achieved by using "mac-base" with a properly
adjusted offset value (0x40 << 16). It may be not pretty but it should
work without custom property or downstream kernel patch to support it.

Cc: Ansuel Smith <[email protected]>
Cc: Catrinel Catrinescu <[email protected]>
Cc: Felix Fietkau <[email protected]>
Signed-off-by: Rafał Miłecki <[email protected]>
Reviewed-by: Rosen Penev <[email protected]>