target/arm: Convert Neon 3-reg-diff long multiplies

target/arm: Convert Neon 3-reg-diff long multiplies

Convert the Neon 3-reg-diff insns VMULL, VMLAL and VMLSL; these perform
a 32x32->64 multiply with possible accumulate.

Note that for VMLSL we do the accumulate directly with a subtraction
rather than doing a negate-then-add as the old code did.

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