apm821xx: add support for the Netgear WNDAP620 and WNDAP660

apm821xx: add support for the Netgear WNDAP620 and WNDAP660

This patch adds support for the Netgear WNDAP620 and WNDAP660,
they are similar devices, but due to the LAN LED configuration,
the switch setup and WIFI configuration each gets a different
device target.

Hardware Highlights WNDAP620:
CPU: AMCC PowerPC APM82181 at 1000 MHz
DRAM:  128 MB, 2 x 64 MiB DDR2 Hynix H5PS5162GF
CPU: AMCC PowerPC APM82181 at 1000 MHz
FLASH: 32 MiB, NAND SLC, Hynix HY27US08561A
Ethernet: RealTek RTL8363SB 2x2-Port Switch PHY - Only 1 GBit Port (POE)
Wifi: Atheros AR9380 minipcie - Dual-Band - 3x3:3
Serial: console port with RJ45 Interface (9600-N-8-1)
LEDS: Power, LAN-Activity, dual color LAN-Linkspeed, 2.4GHz, 5GHz LEDs
Button: Soft Reset Button
Antennae: 3 internal dual-band antennae + 3 x RSMA for external antennaes

Hardware Highlights WNDAP660:
CPU: AMCC PowerPC APM82181 at 1000 MHz + 2 Heatsinks
DRAM:  256 MB, 2 x 128 MiB DDR2
FLASH: 32 MiB, NAND SLC, Hynix HY27US08561A
Ethernet: RealTek RTL8363SB 2x2-Port Switch PHY (POE)
Wifi1: Atheros AR9380 minipcie - Dual-Band - 3x3:3
Wifi2: Atheros AR9380 minipcie - Dual-Band - 3x3:3
Serial: console port with RJ45 Interface (9600-N-8-1)
LEDS: Power, LAN-Activity, 2x dual color LAN-Linkspeed, 2.4GHz, 5GHz LEDs
Button: Soft Reset Button
Antennae: 6 internal dual-band antennae + 3 x RSMA for external antennaes

Flashing requirements:

 - needs a tftp server at 192.168.1.10/serverip.
 - special 8P8C(aka RJ45)<->D-SUB9 Console Cable
   ("Cisco Console Cable"). Note: Both WNDAP6x0 have
   a MAX3232 transceivers, hence no need for any separate
   CMOS/TTL level shifters.

External Antenna:
The antennae mux is controlled by GPIO 11 and GPIO14. Valid Configurations:
 = Config# = | = GPIO 11 = | = GPIO 14 = |  ===== Description =====
      1.     |   1 / High  |  0 / Low    | Use the internal antennae (default)
      2.     |   0 / Low   |  1 / High   | Use the external antennae

The external antennaes are only meant for the 2.4 GHz band.

One-way Flashing instructions via u-boot:

 0. connect the serial cable to the RJ45 Console Port
    Note: This requires a poper RS232 and not a TTL/USB adaptor.

 1. power up the AP and interrupt the u-boot process at

    'Hit any key to stop autoboot'

 2. setup serverip and ipaddr env settings
    Enter the following commands into the u-boot shell
    # setenv ipaddr 192.168.1.1
    # setenv serverip 192.168.1.10

 3. download the factory.img image to the AP
    Enter the following commands into the u-boot shell

    # tftp ${kernel_addr_r} openwrt-apm821xx-nand-netgear_wndap660-squashfs-factory.img

 4. verfiy image integrity
    Enter the following commands into the u-boot shell

    # crc32 $fileaddr $filesize

    If the calculated crc32 checksum does not match, go back to step 3.

 5. flash the image
    Enter the following commands into the u-boot shell

    # nand erase 0x110000 0x1bd0000
    # nand write ${kernel_addr_r} 0x110000 ${filesize}

 6. setup uboot environment
    Enter the following commands into the u-boot shell

    # setenv bootargs
    # setenv fileaddr
    # setenv filesize
    # setenv addroot 'setenv bootargs ${bootargs} root=/dev/ubiblock0_0'
    # setenv owrt_boot 'nboot ${kernel_addr_r} nand0 0x110000; run addroot; run addtty; bootm ${kernel_addr_r}'
    # setenv bootcmd 'run owrt_boot'
    # saveenv

 7. boot
    # run bootcmd

Booting initramfs instructions via u-boot:

 Follow steps 0 - 2 from above.

 3. boot initramfs
    Enter the following commands into the u-boot shell

    # tftp ${kernel_addr_r} openwrt-apm821xx-nand-netgear_wndap660-initramfs-kernel.bin
    # run addtty
    # bootm ${kernel_addr_r}

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
(backported from d82d84694e60d17a79a57fdb135e382f4def907c)