Move libopus SSE4.1 source into the SSE4.1 block.

BUG=webrtc:9530
TEST=cq
R=sergeyu

Change-Id: I7c007d4dfd12aa86a56fccaef176d614531533c2
Reviewed-on: https://chromium-review.googlesource.com/c/1327151
Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606579}
1 file changed