ramips: add support for Sitecom WLR-6000

ramips: add support for Sitecom WLR-6000

The Sitecom firmware upgrade file has SENAO_FIRMWARE_TYPE 2 set. This
looks rather wrong since SENAO_FIRMWARE_TYPE 2 is kernel only but the
file is way to big for only including a kernel.

The factory image need to have the dlf file extension. Otherwise the
Sitecom firmware rejects the file.

The stock firmware uses the following mac addresses:

LAN: 00:0C:F6:AA:BB:D8 (u-boot env: ethaddr)
2,4: 00:0C:F6:AA:BB:D8 (EEPROM)
5:   00:0C:F6:AA:BB:DC (EEPROM)
WAN: 00:0C:F6:AA:C8:43 (u-boot env: wanaddr)

Assuming the mac address range :D8 to :DC is reserved for this device,
the MAC addresses were reorder to have a unique MAC address for each
interface:

2.4GHz: 00:0C:F6:AA:BB:D8
LAN:    00:0C:F6:AA:BB:D9
WAN:    00:0C:F6:AA:BB:DA
5 GHz:  00:0C:F6:AA:BB:DC

The first MAC is assigned to the 2.4GHz WiFi interface
to keep compatibility with the SSIDs printed on the case, which have
the last three sextets of the MAC address appended.

There are still issues with the rt2x00 driver. It is not possible to
use both wireless interfaces at the same time. The 2.4 GHz
wireless (PCIe) only works if the internal 5GHz wireless is/has been
enabled or used for scanning. The internal 5GHz wireless only works if
the 2.4GHz wireless (PCIe) was never enabled. Disabling the 2.4Ghz
after it was enabled will result in stations seeing the 5Ghz AP but are
unable to connect.

Due to the not optimal working wifi the manufacture, backup and storage
partitions of the OEM firmware are kept for now to allow an easy switch
back to the Sitecom firmware.

Signed-off-by: Jasper Scholte <NightNL@outlook.com>
Signed-off-by: Mathias Kresin <dev@kresin.me>