ipq40xx: Convert openmesh,a42 to DSA

ipq40xx: Convert openmesh,a42 to DSA

* ethernet1:

  - physical port label "Ethernet 1"
  - can be used to power the device
  - its mac address is printed on the device label

* ethernet2:

  - physical port label "Ethernet 2"

Both ports are not marked by there role (because the vendor firmware
automatically detects roles) but the "Ethernet 1" port was used in the past
for "WAN" functionality in OpenWrt.

Reviewed-by: Robert Marko <robimarko@gmail.com>
Signed-off-by: Sven Eckelmann <sven@narfation.org>