target-arm: A64: Add SIMD across-lanes instructions

Add support for the SIMD "across lanes" instruction group (C3.6.4).

Signed-off-by: Michael Matz <matz@suse.de>
[PMM: Updated to current codebase, added fp min/max ops,
 added unallocated encoding checks]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
