target-arm: A64 initial decode of data_proc_simd

Due to the complexity of this part of the table the normal extract and
switch approach gets very messy very quickly. This brings in a simple
table based mask/pattern helper for working through the possibilities.

---

v2:
  - change fn typedef to not be ptr
  - add stubs for all exits
  - make failure unallocated (not unsupported)
.travis.yml: add aarch64 targets

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
rm unused field
scripts/qemu-binfmt-conf.sh: re-factor and clean-up

I was looking to set-up for development but found the script made some
hard-coded assumptions. It doesn't seem the script is used by the
distros but if it had a little more love maybe it would be ;-)

* Add usage() instructions
* Move all registering to a single function
* Check for existence of executable qemu before registering
* Add -d (devel) mode for subscribing in-src tree binaries
* error handling when setting binfmt fails
start of simd ldst single structure decode

It's just a stub for now
start of advsimd copy and dup