[llvm] AMDGPU/GlobalISel: Import D16 load patterns and add combines for them (PR #153178)

[Petar Avramovic via llvm-commits]

petar-avramovic wrote:

### Merge activity

* **Sep 11, 10:00 AM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/153178).


https://github.com/llvm/llvm-project/pull/153178