[CMake] Increase timeout for Doxygen runs.

There is no need to limit it to 2 min. For larger modules
like DuMuX this is not enough. Increased timeout to 5 min.

cmake/scripts/RunDoxygen.cmake

 execute_process(COMMAND
   ${DOXYGEN_EXECUTABLE} Doxyfile OUTPUT_FILE doxygen.log ERROR_FILE doxygen.log
-  TIMEOUT 120)
+  TIMEOUT 300)