[SYCL][Doc] Update `sycl_ext_oneapi_root_group.asciidoc` reference (#15917)
# PR Summary
Commit 5d515df02440cde73b85cb2ec0dacf5d68c553c2 moved the
`sycl_ext_oneapi_root_group.asciidoc` to `experimental` section. This PR
adjusts sources to changes.
Signed-off-by: Emmanuel Ferdman <emmanuelferdman@gmail.com>