[SYCL][Doc] Move FPGA extensions (#5470)

Move these two FPGA extensions to the "supported" directory.

Author: gmlueck

sycl/ReleaseNotes.md

@@ -800,7 +800,7 @@ Release notes for commit range 5d7e0925..5eebd1e4bfce
 ### SYCL Compiler
  - Allow for multiple build options for opencl-aot [5e5703f58449]
 ### SYCL Library
- - Implement [`SYCL_INTEL_mem_channel_property`](doc/extensions/MemChannel/SYCL_INTEL_mem_channel_property.asciidoc)
+ - Implement [`SYCL_INTEL_mem_channel_property`](doc/extensions/supported/SYCL_EXT_INTEL_MEM_CHANNEL_PROPERTY.asciidoc)
    extension [2f1f3167b7c6]
  - Add `marray` class as defined by SYCL 2020 provisional [5eebd1e4bfce]
  - Implement dynamic batch size adjusting when using Level-Zero plugin
@@ -1186,7 +1186,7 @@ Release notes for commit range 5976ff0..1fc0e4f
 
 ### Documentation
   - Added documentation for [`SPV_INTEL_usm_storage_classes`](doc/extensions/SPIRV/SPV_INTEL_usm_storage_classes.asciidoc)
-    and [SYCL_INTEL_usm_address_spaces](doc/extensions/USMAddressSpaces/usm_address_spaces.asciidoc) [781fbfc]
+    and [SYCL_INTEL_usm_address_spaces](doc/extensions/supported/SYCL_EXT_INTEL_USM_ADDRESS_SPACES.asciidoc) [781fbfc]
   - Fixed SPIR-V format name spelling [6e9bf3b]
   - Added extension [LocalMemory](doc/extensions/supported/SYCL_EXT_ONEAPI_LOCAL_MEMORY.asciidoc) draft specification [4b5308a]
   - Added extension [free functions queries](doc/extensions/experimental/SYCL_EXT_ONEAPI_FREE_FUNCTION_QUERIES.asciidoc) draft specification [8953bfd]