Improving the AppleTV kernel configuration

@chewitt A lot of the changes are useful, some are debatable and a few are questionable, and should be understood and tested first. I'd like to use this pull-request as a means of discussing them (I am not expecting this PR to be merged, not yet at least). I have added more comments inline in the diff. Feedback welcome !

General changes include:
 - Using a uniprocessor kernel
 - Move all hardware functionality (not provided out-of-the-box) to modules
 - Disable hardware functionality that AppleTV hardware will never support
 - Added hardware functionality in-kernel that AppleTV hardware does have
 - Enable more debugging infrastructure (some intended temporary, other preferred permanent)