cleanup unit_tests/aub_tests/CMakeLists.txt
cleanup unit_tests/elflib/CMakeLists.txt
cleanup unit_tests/libult/CMakeLists.txt
cleanup unit_tests/tbx/CMakeLists.txt
partially cleanup unit_tests/CMakeLists.txt
solution source tree changes:
- make test projects folder as variable
- make platform specific targets folder as variable
- move platform specific targets to \"test platforms\" folder
Change-Id: Iff7da009e13c3ac9e5af76325be32e5056e8cd7b