Clean up armdefs.h a little.

Removes some things we don't even use (ie. related to headers which we don't include/aren't in the repository). Also cleans things up to be slightly more consistent, so that you don't feel like setting fire to your PC every time you need to look up a definition.
Since you're changing them already, change these to `u64`, `u32`, `u8` and `u16`.