target/arm: Pass index to AdvSIMD FCMLA (indexed)

target/arm: Pass index to AdvSIMD FCMLA (indexed)

For aa64 advsimd, we had been passing the pre-indexed vector.
However, sve applies the index to each 128-bit segment, so we
need to pass in the index separately.

For aa32 advsimd, the fp32 operation always has index 0, but
we failed to interpret the fp16 index correctly.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20180627043328.11531-31-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>