Simplify the implementation of mullwo.  For 64 bit CPUs, the result is
the concatenation of the upper and lower parts of the muls2_i32 operation,
which may be slightly better than deposit.  For 32 bit CPUs, the lower part
of the muls_i32 operation is moved into the target GPR.
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>