[llvm] [AMDGPU] Document "relaxed buffer OOB mode", update HSA default (PR #134734)

[Krzysztof Drewniak via llvm-commits]

krzysz00 wrote:

Wanted to ping here - there's been wider discussion about how relaxed buffer OOB mode isn't *really* a subtarget feature

I think it could be made a function attribute - and, more relevantly, should be flipped. The relaxed mode is the expected/default behavior, and the strict mode is only needed to block certain optimizations in some Vulkan contexts - as far as I understand things

https://github.com/llvm/llvm-project/pull/134734