[XLA:GPU] Pass HloInstruction instead of HloComputation to TritonWrapper and TritonIrEmitter.
[XLA:GPU] Pass HloInstruction instead of HloComputation to TritonWrapper and TritonIrEmitter.

This is a preparation for future changes to SymbolicTileAnalysis. 

I plan to make it possible to build SymbolicTileAnalysis from HloFusionAdaptor, so it can be used in Priority Fusion. By design, HloFusionAdaptor should only consist of fusion computations. This change makes sure that we don't pass HloComputation that is not a fusion.
