TD-W8970/8980/9980 UART u-boot image v1.1

Changes:

• simplified build instructions (thanks to Matteo Croce)
• support for generating an u-boot image, which can be written to flash
• switched to the toolchain which is bundled with the GPL sources (requires 32bit build system)

Please note that in case of an UART boot, the CPU will only run at 125MHz. So don't expect it to be as fast as usual.

TD-W8970/8980/9980 UART u-boot image v1.0

initial release