Optimize mulldo by using the muls2_i64 operation rather than a helper.  Eliminate
the obsolete helper code.
Signed-off-by: NTom Musta <tommusta@gmail.com>
Suggested-by: NRichard Henderson <rth@twiddle.net>
Reviewed-by: NRichard Henderson <rth@twiddle.net>
Signed-off-by: NAlexander Graf <agraf@suse.de>