[llvm] [NFC][AMDGPU] Inline `getEffectiveWavesPerEU` (PR #221600)

[Matt Arsenault via llvm-commits]

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@@ -121,15 +121,6 @@ class AMDGPUSubtarget {
   getWavesPerEU(std::pair<unsigned, unsigned> FlatWorkGroupSizes,
                 unsigned LDSBytes, const Function &F) const;
 
-  /// Returns the target minimum/maximum number of waves per EU. This is based
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arsenm wrote:

The point is to keep this a free function that doesn't depend on IR state 

https://github.com/llvm/llvm-project/pull/221600