docs: created separate folder for doxygen config files

Signed-off-by: Mihai Tudor Panu <mihai.tudor.panu@intel.com>

CMakeLists.txt

   # add a target to generate API documentation with Doxygen
   find_package (Doxygen)
   if (DOXYGEN_FOUND)
-    configure_file (${CMAKE_CURRENT_SOURCE_DIR}/Doxyfile.in ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile @ONLY)
+    configure_file (${CMAKE_CURRENT_SOURCE_DIR}/doxy/Doxyfile.in ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile @ONLY)
     add_custom_target (doc
       ${DOXYGEN_EXECUTABLE} ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile
       WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}