[BACKEND] Remove all layout conversion decomposition functions from the NVIDIA backend

[Jokeren]

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[Jokeren]

@binarman Could you please try to remove decompositions from the AMD backend as well?

[binarman]

@Jokeren
hi!
I am currently on vacation and can not do this right away. If this can wait, I will do this when back. If this is needed ASAP, please talk to @antiagainst.

Note: AMD backend has two decompositions used to reduce LDS usage, I think we should leave them(maybe move both of them in pass):

• https://github.com/triton-lang/triton/blob/main/third_party/amd/lib/TritonAMDGPUToLLVM/OptimizeLDSUsage.cpp
• https://github.com/triton-lang/triton/blob/main/third_party/amd/lib/TritonAMDGPUToLLVM/DecomposeUnsupportedConversions.cpp#L46

[Jokeren]

@binarman No worries. Sorry I forgot about that.

@antiagainst It's not urgent but I think it might be better to (1) rename the decomposition functions as there's no "unsupported" conversion anymore, and (2) move the function into the AMD backend only since the NVIDIA backend doesn't use them anymore. WDYT?

[antiagainst]

SG! We'll follow up on cleaning up the corresponding AMD pass afterwards.