This PR introduces 3 new platforms, two from the new Dragonwing IQx
series (QCS615 and QCS8300) as well as the IPQ5424.
Additionally:
* Support for booting downstream Android boot images on some phones is
added
* Capsule update support is expanded to be more generic, determining
which partition U-Boot was flashed to automatically and supporting
many more boards.
* Minor capsule update bugs are fixed
* A watchdog driver is added and gets timeout support
* Autoboot now requires pressing "space" specifically to stop booting as
a workaround for some boards getting rogue key presses which would
cause autoboot to fail
* Documentation is added for the Dragonwing boards
* The RB1/2 now use USB gadget mode rather than host
* A bug is fixed where GPIO reads could return incorrect values