SkSplicer: start on arm64

SkSplicer: start on arm64

Seems to be working.  The jump to loop_start might be a little off, but not by much.  Correctness is really still a big TODO.

$ adb shell 'cd /data/local/tmp; ./monobench SkRasterPipeline 200'
SkRasterPipeline_…
200  …f16_compile 1x  …f16_run 1.42x  …srgb_compile 2.21x  …srgb_run 2.59x⏎

Change-Id: I0e1acc6404cf3ce8084d9ef8011cbe0b5f1fd6e3
Reviewed-on: https://skia-review.googlesource.com/6811
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>