ath79: add support for PISEN WMB001N

ath79: add support for PISEN WMB001N

Specifications:
- SoC: AR9341
- RAM: 64M
- Flash: 16M
- Ethernet: 1 * FE port
- WiFi: ar934x-wmac
- Sound: WM8918 DAC
         1 * 3.5mm headphone jack
         2 * RCA connectors for speakers
         1 * SPDIF out
- USB: 1 * USB2.0 port

Flash instruction:
 Upload generated factory image via vendor's web interface.

Notes:
A. Audio stuff:
 1. Since AR934x, all pins for peripheral blocks can be mapped to
    any available GPIOs. We currently don't have a PCM/I2S driver
    for AR934x so pinmux for i2s and SPDIF are bound to i2c gpio
    node. This should be moved into I2S node when a PCM/I2S driver
    is available.
 2. The i2c-gpio node is for WM8918. DT binding for it can't be added
    currently due to a missing clock from I2S PLL.

B. Factory image:
 Image contains a image header and a tar.gz archive.
 1. Header: A 288 byte header that has nothing to do with appended
    tarball. Format:
     0x0-0x7 and 0x18-0x1F: magic values
     0x20: Model number string
     0xFC: Action string. It's either "update" or "backup"
     0x11C: A 1 byte checksum. It's XOR result of 0x8-0x11B
    Firmware doesn't care about the rest of the header as long as
    checksum result is correct.
    The same header is used for backup and update routines so the
    magic values and model number can be obtained by generating a
    backup bin and grab values from it.
 2. Tarball: It contains two files named uImage and rootfs, which
    will be flashed into corresponding mtd partition.
 Writing a special utility that can only output a fixed binary
 blob is overkill so factory image header is placed under
 image/bin instead.

C. LED
 The wifi led has "Wi-Fi" marked on the case but vendor's firmware
 used it as system status indicator. I did the same in this device
 support patch.

D. Firmware
 Factory u-boot is built without 'savenv' support so it's impossible
 to change kernel offset. A 2MB kernel partition won't be enough in
 the future. OKLI loader is used here to migrate this problem:
  1. add OKLI image magic support into uImage parser.
  2. build an OKLI loader, compress it with lzma and add a normal
     uImage header.
  3. flash the loader to where the original kernel supposed to be.
  4. create a uImage firmware using OKLI loader.
  5. flash the created firmware to where rootfs supposed to be.
 By doing so, u-boot will start OKLI loader, which will then load
 the actual kernel at 0x20000.

 The kernel partition is 2MB, which is too much for our loader.
 To save this space, "mtd-concat" is used here:
  1. create a 64K (1 erase block) partition for OKLI loader and
     create another partition with the left space.
  2. concatenate rootfs and this partition into a virtual flash.
  3. use the virtual flash for firmware partition.

 Currently OKLI loader is flashed with factory image only.
 sysupgrade won't replace it. Since it only has one function
 and it works for several years, its unlikely to have some bugs
 that requires a replacement.

Signed-off-by: Chuanhong Guo <gch981213@gmail.com>