[tilegx] Initial support for SIMD.

  Including register define, add/sub basic instruction support.
Expand unsupported vector operations.

  TILE-Gx do not have complete SIMD support for a given vector type,
for example v2i32. Thus, we need to expand those unsupported vector
operations into scalar instructions.
[tilegx] Initial Intrinsic support.

  * enable tilegx support in llvm's intrinsic framework.
  * support add/sub with testing purpose.
[tilegx] Initial support for TargetTransformInfo.

  We need TILE-Gx TargetTransformInfo implementation to support
auto-vectorize and several other IR level transformations,
[tilegx] Intrinsic support for all TILE-Gx SIMD.

   * support all instructions documented at:
       http://www.tilera.com/scm/docs/UG401-ISA.pdf, chapter 14