target/arm/vec_helper: Handle oprsz less than 16 bytes in indexed operations

target/arm/vec_helper: Handle oprsz less than 16 bytes in indexed operations

In the gvec helper functions for indexed operations, for AArch32
Neon the oprsz (total size of the vector) can be less than 16 bytes
if the operation is on a D reg. Since the inner loop in these
helpers always goes from 0 to segment, we must clamp it based
on oprsz to avoid processing a full 16 byte segment when asked to
handle an 8 byte wide vector.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20200828183354.27913-43-peter.maydell@linaro.org