perf annotate: Return arch from symbol__disassemble() and save it in browser

In annotate browser, we will add support to check fused instructions.
While this is x86-specific feature so we need the annotate browser to
know what the arch it runs on.

symbol__disassemble() has figured out the arch. This patch just lets the
arch return from symbol__disassemble and save the arch in annotate
browser.

Signed-off-by: Yao Jin <yao.jin@linux.intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1497840958-4759-2-git-send-email-yao.jin@linux.intel.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>