Rename GPUXToSPIRV Pass to GPUToSPIRVExt

[drprajap]

GPUXToSPIRV pass is just extension to upstream GPUTOSPIRV pass, it does not use with GPUX dialect, so this patch is correcting the misleading pass name.

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[nbpatel]

ConvertGPUToSPIRVDialectPass maybe? SPIRVExt seems a little misleading

[drprajap]

ConvertGPUToSPIRVDialectPass maybe? SPIRVExt seems a little misleading

yes SPIRVExt seems confusing, have to think about other name, I have not seen somethingDialectPass for conversion passes, but will check in upstream and see.