ramips: add support for MTC Wireless Router WR1201

ramips: add support for MTC Wireless Router WR1201

MTC Wireless Router WR1201 is the OEM name of the board. It is also sold
rebranded as STRONG Dual Band Gigabit Router 1200.

Specification:
- SoC: MediaTek MT7621A (880 MHz)
- Flash: 16 MiB
- RAM: 128 MiB
- Wireless: 2.4Ghz(MT7602EN) and 5Ghz (MT7612EN)
- Ethernet speed: 10/100/1000
- Ethernet ports: 4+1
- 1x USB 3.0
- 1x microSD reader
- Serial baud rate of Bootloader and factory firmware: 57600

The OEM webinterface writes only as much bytes as listed in the
uImage header field to the flash. Also, the OEM webinterface
evaluates the name field of uImage header before flashing (the
string "WR1201_8_128")

To flash via webinterface, is mandatory to use first initramfs.bin
and after (from the OpenWrt) the sysupgrade.bin

Some notes:
- Some microSD will not work:

  mtk-sd 1e130000.sdhci: no support for card's volts
  mmc0: error -22 whilst initialising SDIO card
  mtk-sd 1e130000.sdhci: no support for card's volts
  mmc0: error -22 whilst initialising MMC card
  mtk-sd 1e130000.sdhci: no support for card's volts
  mmc0: error -22 whilst initialising SDIO card
  mtk-sd 1e130000.sdhci: card claims to support voltages below defined range
  mtk-sd 1e130000.sdhci: no support for card's volts
  mmc0: error -22 whilst initialising MMC card
  mtk-sd 1e130000.sdhci: no support for card's volts
  mmc0: error -22 whilst initialising SDIO card
  mtk-sd 1e130000.sdhci: no support for card's volts
  mmc0: error -22 whilst initialising MMC card

Signed-off-by: Valentín Kivachuk <vk18496@gmail.com>