Doxygen comments for avxintrin.h.

Doxygen comments for avxintrin.h.

Added doxygen comments to avxintrin.h's intrinsics. As of now, around 75% of the
intrinsics in this file are documented here. The patches for the other 25% will be se
nt out later.

Removed extra spaces in emmitrin.h.

Note: The doxygen comments are automatically generated based on Sony's intrinsics document.

I got an OK from Eric Christopher to commit doxygen comments without prior code
review upstream.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@286336 91177308-0d34-0410-b5e6-96231b3b80d8