[DOXYGEN] Updated instruction names corresponding to avxintrin.h intrinsics.

Documentation for some of the avxintrin.h's intrinsics errorneously said that
non VEX-prefixed instructions could be generated. This was fixed.

I tried several different solutions to achieve pretty printing of unordered lists (nested and non-nested) in param sections in doxygen. 

llvm-svn: 287990