target/arm: Implement MVE VCLZ

target/arm: Implement MVE VCLZ

Implement the MVE VCLZ insn (and the necessary machinery
for MVE 1-input vector ops).

Note that for non-load instructions predication is always performed
at a byte level granularity regardless of element size (R_ZLSJ),
and so the masking logic here differs from that used in the VLDR
and VSTR helpers.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210617121628.20116-4-peter.maydell@linaro.org