[llvm] [AMDGPU][Draft] OOB mode - module flag (PR #160922)

[Piotr Sobczak via llvm-commits]

piotrAMD wrote:

Split amdgpu.oob.mode to `amdgpu.buffer.oob.relaxed`/`amdgpu.buffer.oob.relaxed` as bitfields cannot be supported in the linking behavior.
Addressed review feedback to return enum default value.
Update tests.
Fixed docs formatting.

https://github.com/llvm/llvm-project/pull/160922