target/arm: Fix alignment for VLD4.32

target/arm: Fix alignment for VLD4.32

When requested, the alignment for VLD4.32 is 8 and not 16.

See ARM documentation about VLD4 encoding:
    ebytes = 1 << UInt(size);
    if size == '10' then
        alignment = if a == '0' then 1 else 8;
    else
        alignment = if a == '0' then 1 else 4*ebytes;

Signed-off-by: Clément Chigot <chigot@adacore.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220914105058.2787404-1-chigot@adacore.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>