x86/cpu: Clean up modalias feature matching

We currently include commas on both sides of the feature ID in a
modalias, but this prevents the lowest numbered feature of a CPU from
being matched.  Since all feature IDs have the same length, we do not
need to worry about substring matches, so omit commas from the
modalias entirely.

Avoid generating multiple adjacent wildcards when there is no
feature ID to match.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Acked-by: Thomas Renninger <trenn@suse.de>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>