AMDGPU/SI: Add d16 support for image intrinsics.

Summary:
  This patch implements d16 support for image load, image store and image sample intrinsics.

Reviewers:
  Matt, Brian.

Differential Revision:
  https://reviews.llvm.org/D3991

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@322903 91177308-0d34-0410-b5e6-96231b3b80d8
11 files changed