ath79: Port PowerCloud Systems CR5000 support

ath79: Port PowerCloud Systems CR5000 support

Add ath79 arch support for PowerCloud Systems CR5000.  Previously
supported under ar71xx (however there are some errors in that support;
to be fixed shortly).

Info:

* This board is based on the Atheros DB120 reference design, but doesn't
  use the on-board switch.  Instead it attachs GMAC0 to an AR8327 switch.
* It only uses GMAC0 and the WAN is simply a VLAN in the stock firmware.
* It has 64MB RAM and 8MB flash.
* In the dts version we get rid of using 'open-drain' for the AR8327
  LED controls.
* As with the platform data version we disable JTAG as this conflicts
  with one of the pair of GPIO's required for the power/status LED
  (GPIO2 and GPIO4 are used for this LED).
* The pcie card wifi has an EEPROM but gets it's MAC address from
  the ART partition.
* The SoC wifi (2.4 GHz) is all from the ART.
* The USB is support comes from the SoC.

NB. This is actually an AR9342 rather than AR9344 but we use the 9344
definitions because there are no relevant differences for this board.

NB: Building only images that don't support reverting to the old
cloud-based firmware as the Skydog cloud service for the CR5000 no
longer exists.

Signed-off-by: Daniel F. Dickinson <cshored@thecshore.com>