[Hexagon] Generate HVX code for vector construction and access

Support for:
  - build vector,
  - extract vector element, subvector,
  - insert vector element, subvector,
  - shuffle.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@319901 91177308-0d34-0410-b5e6-96231b3b80d8
23 files changed