ipq40xx: Add support for Linksys EA8300 (Dallas)

ipq40xx: Add support for Linksys EA8300 (Dallas)

The Linksys EA8300 is based on QCA4019 and QCA9888 and provides three,
independent radios. NAND provides two, alternate kernel/firmware
images with fail-over provided by the OEM U-Boot.

Installation:

  "Factory" images may be installed directly through the OEM GUI.

Hardware Highlights:

  * IPQ4019 at 717 MHz (4 CPUs)
  * 256 MB NAND (Winbond W29N02GV, 8-bit parallel)
  * 256 MB RAM
  * Three, fully-functional radios; `iw phy` reports (FCC/US, -CT):
      * 2.4 GHz radio at 30 dBm
      * 5 GHz radio on ch. 36-64 at 23 dBm
      * 5 GHz radio on ch. 100-144 at 23 dBm (DFS), 149-165 at 30 dBm
      #{ managed } <= 16, #{ AP, mesh point } <= 16, #{ IBSS } <= 1
      * All two-stream, MCS 0-9
  * 4x GigE LAN, 1x GigE Internet Ethernet jacks with port lights
  * USB3, single port on rear with LED
  * WPS and reset buttons
  * Four status lights on top
  * Serial pads internal (unpopulated)

  "Linksys Dallas WiFi AP router based on Qualcomm AP DK07.1-c1"

Implementation Notes:

  The OEM flash layout is preserved at this time with 3 MB kernel and
  ~69 MB UBIFS for each firmware version. The sysdiag (1 MB) and
  syscfg (56 MB) partitions are untouched, available as read-only.

Serial Connectivity:

  Serial connectivity is *not* required to flash.

  Serial may be accessed by opening the device and connecting
  a 3.3-V adapter using 115200, 8n1. U-Boot access is good,
  including the ability to load images over TFTP and
  either run or flash them.

  Looking at the top of the board, from the front of the unit,
  J3 can be found on the right edge of the board, near the rear

      |
   J3 |
  |-| |
  |O| | (3.3V seen, open-circuit)
  |O| | TXD
  |O| | RXD
  |O| |
  |O| | GND
  |-| |
      |

Unimplemented:

    * serial1 "ttyQHS0" (serial0 works as console)
    * Bluetooth; Qualcomm CSR8811 (potentially conected to serial1)

Other Notes:

    https://wikidevi.com/wiki/Linksys_EA8300 states

        FCC docs also cover the Linksys EA8250. According to the
	RF Test Report BT BR+EDR, "All models are identical except
	for the EA8300 supports 256QAM and the EA8250 disable 256QAM."

Signed-off-by: Jeff Kletsky <git-commits@allycomm.com>