Add kvmclock timer to documentation, schema and parsers.  Keep the
platform timer first since it is kind of special, and alphabetize
the others when possible (i.e. when it does not change the ABI).
Reviewed-by: NJiri Denemark <jdenemar@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>