Add a scalarize llvm pass.

Add a scalarize llvm pass.

In previous implementation expand vector ops in GenWrite,
it is hard to optimize. Now, I add new llvm pass to scalarize.
This pass will expand all normal vector ops to scalar ops,
except store/load, image read/write and function's argument.
Add fake ExtractElement/InsertElement instructions to avoid
dead instruction elimination, and unit valueMap hold the
relationship between these fake instructions and real
load/store instructions.

Signed-off-by: Yang Rong <rong.r.yang@intel.com>
Reviewed-by: Zhigang Gong <zhigang.gong@linux.intel.com>