target/arm: Merge helper_sve_clr_* and helper_sve_movz_*

target/arm: Merge helper_sve_clr_* and helper_sve_movz_*

The existing clr functions have only one vector argument, and so
can only clear in place.  The existing movz functions have two
vector arguments, and so can clear while moving.  Merge them, with
a flag that controls the sense of active vs inactive elements
being cleared.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20200815013145.539409-10-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>