[NFC][SYCL][Joint Matrix] Added licence header to tests

[artemrad]

No description provided.

[YuriPlyakhin]

need to make the file headers consistent with the coding standard https://llvm.org/docs/CodingStandards.html#file-headers

The other point from the coding standard:
If you are extending, enhancing, or bug fixing already implemented code, use the style that is already being used so that the source is uniform and easy to follow.

Hence, I suggest just follow what we are already using in https://github.com/intel/llvm/tree/sycl/sycl/test-e2e/Matrix, which is

//==----------- element_wise_abc.cpp - DPC++ joint_matrix------------- ----==//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

[YuriPlyakhin]

Please, resolve formatting problem. thanks.

[YuriPlyakhin]

LGTM.
Please, add [NFC] tag to the title of your PR.

[artemrad]

@intel/llvm-gatekeepers the PR is ready.