target-arm: A64: Add SIMD ZIP/UZP/TRN

Add support for the SIMD ZIP/UZIP/TRN instruction group
(C3.6.3).

Signed-off-by: Michael Matz <matz@suse.de>
[PMM: use new do_vec_get/set etc functions and generally update to new
 codebase standards; refactor to pull per-element loop outside switch]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
