[NVPTX] Add prefetch tensormap variant (#146203)
[NVPTX] Add Prefetch tensormap intrinsics
This PR adds prefetch intrinsics with the relevant tensormap_space.
* Lit tests are added as part of prefetch.ll
* The generated PTX is verified with a 12.3 ptxas executable.
* Added docs for these intrinsics in NVPTXUsage.rst.
For more information, refer to the PTX ISA for prefetch intrinsic :
[Prefetch
Tensormap](https://docs.nvidia.com/cuda/parallel-thread-execution/#data-movement-and-conversion-instructions-prefetch-prefetchu)
@durga4github @schwarzschild-radius
