ipq40xx: Convert mikrotik,wap-ac to DSA

ipq40xx: Convert mikrotik,wap-ac to DSA

As done previously, this preserves the MAC addresses of they physical
Ethernet ports. The interfaces are renamed as eth0 is in use for the
native GMAC; the new interface naming matches the physical port labels.
 - sw-eth1 corresponds to the physical port labeled ETH1 and has the
   base MAC address. This port can be used to power the device.
 - sw-eth2 corresponds to the physical port labeled ETH2 and has a MAC
   address one greater than the base.

As this device has 2 physical ports, they are each connected to their
respective PHYs, allowing the link status to be visible to software.
Since they are not marked on the case with any role (such as LAN or
WAN), both are bridged to the lan network by default, although this can
easily be changed if needed.

Signed-off-by: Mark Mentovai <mark@mentovai.com>