Hexagon HVX (target/hexagon) fix bug in HVX saturate instructions

Two tests added to tests/tcg/hexagon/hvx_misc.c
    v21.uw = vadd(v11.uw, v10.uw):sat
    v25:24.uw = vsub(v17:16.uw, v27:26.uw):sat

Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>
Message-Id: <20220210021556.9217-3-tsimpson@quicinc.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>