amazon-tate: new device

This MR adds support for the Amazon Kindle Fire HD ('amazon-tate').

Working:

• Charging
• Display
• Touchscreen (although loading module adds about 30 sec to boot times)
• USB networking

Untested:

• HDMI out

Currently broken:

• Audio (hangs kernel when anything tries to access it)
• Wi-Fi (may be possible to re-use the f/w from firmware-amazon-soho, needs checking)
• GPU acceleration (very unlikely to be resolved, PowerVR SGX based)
• Camera

This port is able to get to a framebuffer XFCE session currently, but not much more than that.

Users need to install the 'console' rootfs and bootstrap XFCE from there, the stock bootloader can't handle flashing rootfs images larger than around ~900MB via fastboot and sparse seems to be broken.

Install process still needs to be updated on the wiki.

Tate relies on a second copy of u-boot to run unsigned code/recovery, hidden at the top of the boot partition. As long as we keep the boot img below ~7.5MB we shouldn't clobber it using fastboot. Ideally we build this second copy of u-boot ourselves but work still needs to be done on that.