[llvm] [SPIR-V] Extend SPIRVUsage.rst document (PR #84744)

[Arvind Sudarsanam via llvm-commits]

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@@ -108,3 +179,210 @@ dimensionality parameter as ``1`` meaning 2D. Sampled image types include the
 parameters of its underlying image type, so that a sampled image for the
 previous type has the representation
 ``target("spirv.SampledImage, void, 1, 1, 0, 0, 0, 0, 0)``.
+
+.. _spirv-intrinsics:
+
+LLVM IR Intrinsics
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asudarsa wrote:

Sub-topic can be 'SPIR-V friendly LLVM IR intrinsics'?

https://github.com/llvm/llvm-project/pull/84744