ramips: add support for HooToo HT-TM05

ramips: add support for HooToo HT-TM05

The HooToo HT-TM05 is a battery powered router, with an Ethernet and USB port.
Vendor U-Boot limited to 1.5 MB kernel size, so use lzma loader (loader-okli).

Specifications:

  SOC:     MediaTek MT7620N
  BATTERY: 10400mAh
  WLAN:    802.11bgn
  LAN:     1x 10/100 Mbps Ethernet
  USB:     1x USB 2.0 (Type-A)
  RAM:     64 MB
  FLASH:   GigaDevice GD25Q64, Serial 8 MB Flash, clocked at 50 MHz
           Flash itself specified to 80 MHz, but speed limited by mt7620 SPI
           fast-read enabled (m25p)
  LED:     Status LED (blue after boot, green with WiFi traffic
           4 leds to indicate power level of the battery (unable to control)
  INPUT:   Power, reset button

MAC assignment based on vendor firmware:

  2.4 GHz    *:b4   (factory 0x04)
  LAN/label  *:b4   (factory 0x28)
  WAN        *:b5   (factory 0x2e)

Tested and working:

 - Ethernet
 - 2.4 GHz WiFi (Correct MAC-address)
 - Installation from TFTP (recovery)
 - OpenWRT sysupgrade (Preserving and non-preserving), through the usual
   ways: command line and LuCI
 - LEDs (except as noted above)
 - Button (reset)
 - I2C, which is needed for reading battery charge status and level
 - U-Boot environment / variables (from U-Boot, and OpenWrt)

Installation:

 - Download the needed OpenWrt install files, place them in the root
   of a clean TFTP server running on your computer. Rename the files as,
   - ramips-mt7620-hootoo_tm05-squashfs-kernel.bin => kernel
   - ramips-mt7620-hootoo_tm05-squashfs-rootfs.bin => rootfs
 - Plug the router into your computer via Ethernet
 - Set your computer to use 10.10.10.254 as its IP address
 - With your router shut down, hold down the power button until the first
   white LED lights up.
 - Push and hold the reset button and release the power button. Continue
   holding the reset button for 30 seconds or until it begins searching
   for files on your TFTP server, whichever comes first.
 - The router (10.10.10.128) will look for your computer at 10.10.10.254
   and install the two files. Once it has finished installation, it will
   automatically reboot and start up OpenWrt.
 - Set your computer to use DHCP for its IP address

Notes:

 - U-Boot environment can be modified, u-boot-env is preserved on initial
   install or sysupgrade
 - mtd-concat functionality is included, to leave a "hole" for u-boot-env,
   combining the OEM kernel and rootfs partitions

I would like to thank @mpratt14 and @xabolcs for their help getting the
lzma loader to work!

Signed-off-by: Russell Morris <rmorris@rkmorris.us>
[drop changes in image/Makefile, fix indent and PKG_RELEASE in
uboot-envtools, fix LOADER_FLASH_OFFS, minor commit message facelift,
add COMPILE to Device/Default]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>