Documentation: kvm: Convert cpuid.txt to .rst

Convert cpuid.txt to .rst format to be parsable by sphinx.

Change format and spacing to make function definitions and return values
much more clear. Also added a table that is parsable by sphinx and makes
the information much more clean. Updated Author email to their new
active email address. Added license identifier with the consent of the
author.

Signed-off-by: Luke Nowakowski-Krijger <lnowakow@eng.ucsd.edu>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>