target/arm: Convert Neon 3-reg-diff saturating doubling multiplies

target/arm: Convert Neon 3-reg-diff saturating doubling multiplies

Convert the Neon 3-reg-diff insns VQDMULL, VQDMLAL and VQDMLSL:
these are all saturating doubling long multiplies with a possible
accumulate step.

These are the last insns in the group which use the pass-over-each
elements loop, so we can delete that code.

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