target-arm: A64: Add saturating int ops (SQNEG/SQABS)

This mostly re-uses the existing NEON helpers with an additional two for
the 64 bit case. I also took the opportunity to add TCG_CALL_NO_RWG
options to the helpers as they don't modify globals (saturation flags
are in the CPU Environment).

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
target-arm: A64: Add saturating accumulate ops (USQADD/SUQADD)

I've added a new set of helpers to do the saturating add operations as
these are not covered by existing NEON instructions.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

---
v2
  - shorted test for overflow in 64 bit cases
  - added TCG_CALL_NO_RWG flags to helpers
  - common macros, cleaned up
translate-a64.c: add a debug helper trace macro

This just makes it easier to drop TRACE_DECODE statements all over the
place instead of fprintfs.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

---

v2 (ajb)
   - checkpatch.pl fixes
qemu-log: support simple pid substitution in logfile

When debugging stuff that occurs over several forks it would be useful
not to keep overwriting the one logfile you've set-up. This allows a
simple %d to be included once in the logfile parameter which is
substituted with getpid().
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
* add support for aarch64
scripts/qemu-binfmt-check.py: a binfmt checker

This script allows you to check if a given binary will match against any
of the currently registered binfmts on the system.

---

v2 (ajb):
   - cleaned up whitespace and checkpatch fixes
v3 (ajb)):
   - usage() and logging clean-ups
tcg: add tcg_abort_dbg() for additional debug info

There are times the tcg aborts with a fatal but terse error which isn't
overly helpful. This adds an alternative macro that can be used to show
a little more helper information when an abort occurs.
tcg: add debug helpers tcg_debug_dump_i(32|64)

The helpers are useful for debugging if you want to inspect interim
values of tcg temp variables while executing TCG generated code. This is
an alternative to tracing with logs or inspecting with GDB.

The functions do take format strings but to prevent massive memory loss
it will default to a constant string after a short number of uses.