[SYCL][Fusion] Document unsupported features (#11705)

Document SYCL features currently not supported by kernel fusion in the
implementation documentation.

---------

Signed-off-by: Lukas Sommer <[email protected]>

Author: sommerlukas

sycl/doc/design/KernelFusionJIT.md

@@ -2,8 +2,7 @@
 
 ## Context
 
-To support the [user driven kernel fusion extension](https://github.com/intel/llvm/pull/7098) (a presentation can be found [here](https://github.com/oneapi-src/oneAPI-tab/blob/main/tab-dpcpp-onedpl/presentations/oneAPI-TAB-20220727-Kernel-Fusion.pdf)).
-Currently, only targets able to consume SPIR-V are supported.
+To support the [user driven kernel fusion extension](https://github.com/intel/llvm/pull/7098) (a presentation can be found [here](https://github.com/oneapi-src/oneAPI-tab/blob/main/language/presentations/oneAPI-TAB-20220727-Kernel-Fusion.pdf)).
 
 The basic workflow is shown in the diagram below
 
@@ -284,3 +283,13 @@ flag during static compilation.
 During the fusion process at runtime, the JIT will load the LLVM IR and
 finalize the fused kernel to the final target. More information is available
 [here](./CompilerAndRuntimeDesign.md#kernel-fusion-support).
+
+### Unsupported SYCL constructs
+
+The following SYCL API constructs are currently not officially supported for
+kernel fusion and should be considered untested/unsupported: 
+
+- Reductions
+- `sycl::stream`
+- Specialization constants and `sycl::kernel_handler`
+- Images (`sycl::unsampled_image` and `sycl::sampled_image`)

sycl/doc/extensions/experimental/sycl_ext_codeplay_kernel_fusion.asciidoc

@@ -73,12 +73,6 @@ on an API for kernel fusion in SYCL to inform a future extension proposal
 addressing the mentioned problems. 
 ====
 
-[NOTE]
-====
-This extension is currently being implemented in {dpcpp} only for kernels in
-SPIRV format.
-====
-
 == Overview
 
 Every kernel launch in SYCL carries an overhead due to memory traffic and device