[llvm] [AMDGPU] Move tryEffectiveStall to GCNSchedStrategy class, optionally use in tryPendingCandidate (PR #191924)

[Robert Imschweiler via llvm-commits]

ro-i wrote:

Shouldn't the test show what the option/`tryEffectiveStall` is doing?
Also, why is this behind an option at all?

https://github.com/llvm/llvm-project/pull/191924