target-arm: A64: Add "Floating-point data-processing (3 source)" insns

target-arm: A64: Add "Floating-point data-processing (3 source)" insns

This patch adds emulation for the "Floating-point data-processing (3 source)"
group of instructions.

Signed-off-by: Alexander Graf <agraf@suse.de>
[WN: Commit message tweak, merged single and double precision patches.
 Implement using muladd as suggested by Richard Henderson.]
Signed-off-by: Will Newton <will.newton@linaro.org>
[PMM: pull field decode up a level, use register accessors]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>