amazon-douglas: initial support

First port of amazon-douglas to postmarketOS by me.

• Used kernel source and config from the Fire_HD8_7th_Gen-5.3.7.1-20200323.tar.bz2 release.

What works:

• Boots
• Weston
  • Display
  • Touch
• USB Networking

What doesn't:

• USB OTG?
• WiFi
• Plasma mobile: lightdm fails to launch
• xfce4: After launching and touching the screen causes a system hang

What's weird

• Flashing: I followed the instructions for suez. Specifically, I sideloaded a recovery.zip via TWRP. This recovery.zip was custom patched with references to the boot partition label being replaced by boot_x. I kind of understand why this is done but not really.
• Multi core: cpu1-3 keeps enabling and disable themselves. cpu0 remain active at all times.