include: Add missing DNNL_EXPERIMENTAL_UKERNEL ifdef

[mgorny]

Description

Add a missing #ifdef DNNL_EXPERIMENTAL_UKERNEL around dnnl_api_utils group. The templates inside that group reference dnnl_brgemm_t and dnnl_brgemm_pack_B_t types that are guarded using the same condition, and therefore attempting to include the file without the define results in errors:

/home/mgorny/miniforge3/envs/pytorch/include/oneapi/dnnl/dnnl_ukernel.hpp:38:22: error: ‘dnnl_brgemm_t’ was not declared in this scope; did you mean ‘dnnl_stream_t’?
   38 | struct handle_traits<dnnl_brgemm_t> {
      |                      ^~~~~~~~~~~~~
      |                      dnnl_stream_t
/home/mgorny/miniforge3/envs/pytorch/include/oneapi/dnnl/dnnl_ukernel.hpp:38:35: error: template argument 1 is invalid
   38 | struct handle_traits<dnnl_brgemm_t> {
      |                                   ^
/home/mgorny/miniforge3/envs/pytorch/include/oneapi/dnnl/dnnl_ukernel.hpp:45:22: error: ‘dnnl_brgemm_pack_B_t’ was not declared in this scope
   45 | struct handle_traits<dnnl_brgemm_pack_B_t> {
      |                      ^~~~~~~~~~~~~~~~~~~~
/home/mgorny/miniforge3/envs/pytorch/include/oneapi/dnnl/dnnl_ukernel.hpp:45:42: error: template argument 1 is invalid
   45 | struct handle_traits<dnnl_brgemm_pack_B_t> {
      |                                          ^

Checklist

General

• Do all unit and benchdnn tests (make test and make test_benchdnn_*) pass locally for each commit?
• Have you formatted the code using clang-format?

Performance improvements

• Have you submitted performance data that demonstrates performance improvements?

New features

• Have you published an RFC for the new feature?
• Was the RFC approved?
• Have you added relevant tests?

Bug fixes

• Have you included information on how to reproduce the issue (either in a github issue or in this PR)?
• Have you added relevant regression tests?

RFC PR

• Does RFC document follow the template?
• Have you added a link to the rendered document?

[vpirogov]

make test