Hook up vp8_diamond_search_sad_sse3

Hook up vp8_diamond_search_sad_sse3

The original commit never set any 'specialize' line:
61311e61039c300ae872ccba22304e9e60dc0205

It appears the sadx4 version of function uses sdx4df calls to speed up
the search. There are no sse3 versions of the sdx4df functions, but
there are sse2 and msa versions.

There is a neon version of vpx_sad16x16x4d but not any of the smaller
versions. Perhaps if they existed this function could be expanded to use
them.

Change-Id: I936d7d6b1a3ff6dcd5a4d2322272708c47cdec13