[llvm] [SPIR-V] Update docs to describe support of SPV_KHR_shader_clock (PR #93168)

[Michal Paszkowski via llvm-commits]

https://github.com/michalpaszkowski approved this pull request.

@VyacheslavLevytskyy Thank you for catching this and updating!

https://github.com/llvm/llvm-project/pull/93168