http://www.law.cornell.edu/uscode/html/uscode17/usc_sec_17_0...
Doesn't look to me like it covers CPU features.
Copyright is about the right to restrict copying - the clue is in the name. The software case is fundamentally different, because your computer must make a (temporary) copy of the software in order to use it.
(On the other hand, if they designed it such that you needed to upload a piece of (copyrighted) microcode to the CPU on each boot, then that could well bring it within the remit of copyright law. In that case, if you wanted to produce a third-party version, you'd have to write your own "clean room" version of the necessary microcode, which seems like a pretty high hurdle).
http://en.wikipedia.org/wiki/Lexmark_Int%27l_v._Static_Contr...
Lexmark lost.