[DFT][CMake] Fix inclusion of public include directories when linking against a DFT backend library

[hjabird]

Description

This PR ensures that linking against backend such as target_link_library(myApp PRIVATE onemkl_dft_cufft correctly includes the oneMKL public include directories.

Fixes #442

Checklist

All Submissions

• Do all unit tests pass locally? Attach a log.
  • onemklinteldft.txt
  • onemklrocmdft.txt
  • onemklcufftdft.txt
  • onemklcudadft_rebase.txt for after rebase, including CT example with MKLCPU DFT and CUFFT.
  • Tests build and run with portFFT, but some test cases failed. The changes in this PR should not be related to these problems.
• [N/A] Have you formatted the code using clang-format?

Bug fixes

• [ish] Have you added relevant regression tests?
  • The compile-time DFT example has been modified to depend on the described functionality.
• Have you included information on how to reproduce the issue (either in a
  GitHub issue or in this PR)?

[hjabird]

This affects only the build, so pinging @vmalia.

[hjabird]

I'm told I pinged the wrong person - sorry vmalia! @mkrainiuk

[mkrainiuk]

Looks good to me, thank you! I have one minor question.