ath79: add support for Netgear WNDR4300 v2

ath79: add support for Netgear WNDR4300 v2

This patch introduces support for Netgear WNDR4300v2.

Specification
=============
  * Description: Netgear WNDR4300 v2
  * Loader: U-boot
  * SOC: Qualcomm Atheros QCA9563 (775 MHz)
  * RAM: 128 MiB
  * Flash: 2 MiB SPI-NOR + 128 MiB SPI-NAND
	- NOR: U-boot binary: 256 KiB
	- NOR: U-boot environment: 64 KiB
	- NOR: ART Backup: 64 KiB
 	- NOR: Config: 64 KiB
	- NOR: Traffic Meter: 64 KiB
	- NOR: POT: 64 KiB
	- NOR: Reserved: 1408 KiB
	- NOR: ART: 64 KiB
	- NAND: Firmware: 25600 KiB (see notes for OpenWrt)
	- NAND: Language: 2048 KiB
	- NAND: mtdoops Crash Dump: 128 KiB
	- NAND: Reserved: 103296 KiB
  * Ethernet: 5 x 10/100/1000 (4 x LAN, 1 x WAN) (AR8337)
  * Wireless:
	- 2.4 GHz b/g/n (internal)
	- 5 GHz a/n (AR9580)
  * USB: yes, 1 x USB 2.0
  * Buttons:
	- Reset
	- WiFi (rfkill)
	- WPS
  * LEDs:
	- Power (amber/green)
	- WAN (amber/green)
	- WLAN 2G (green)
	- WLAN 5G (blue)
	- 4 x LAN (amber/green)
	- USB (green)
	- WPS (green)
  * UART: 4-pin connector JP1, 3.3V (Vcc, TX, RX, GND), 115200 8N1
  * Power supply: DC 12V 1.5A
  * MAC addresses: LAN=WLAN2G on case label, WAN +1, WLAN5G +2

Important Notes
===============
0. NOR Flash (2 MiB) is not touched by OpenWrt installation.
1. NAND Flash (128 MiB) layout under OpenWrt is changed as follows:
   all space is split between 4 MiB kernel and 124 MiB UBI areas;
   vendor partitions (language and mtdoops) are removed; kernel space
   size can be further expanded if needed; maximum image size is set
   to 25600k for compatibility reasons and can also be increased.
2. CPU clock is 775 MHz, not 750 MHz.
3. 5 GHz wireless radio chip is Atheros AR9580-AR1A with bogus PCI
   device ID 0xabcd. For ath9k driver to load successfully, this is
   overriden in DTS with correct value for this chip, 0x0033.
4. RFKILL button is wired to AR9580 pin 9 which is normally disabled
   by chip definition in ath9k code (0x0000F4FF gpio mask). Therefore
   'qca,gpio-mask=<0xf6ff>' hack must be used for button to work
   properly.
5. USB port is always on, no GPIO for 5V power control has been
   identified.

Installation
============
  * TFTP recovery
  * TFTP via U-boot prompt
  * sysupgrade
  * Web interface

Test build configuration
========================
CONFIG_TARGET_ath79=y
CONFIG_TARGET_ath79_nand=y
CONFIG_TARGET_ath79_nand_DEVICE_netgear_wndr4300-v2=y
CONFIG_ALL_KMODS=y
CONFIG_DEVEL=y
CONFIG_CCACHE=y
CONFIG_COLLECT_KERNEL_DEBUG=y
CONFIG_IMAGEOPT=y

Signed-off-by: Michal Cieslakiewicz <michal.cieslakiewicz@wp.pl>