Build: Fix missing Cmake command win_fix_dir_sep

Adds include of Utils.cmake to FindPlantUML.cmake. Solves the
building error `Unknown CMake command win_fix_dir_sep`.

Change-Id: Iaed5a6cc92e96832e668f32065d73d28d59033e5
Signed-off-by: Tudor Cretu <tudor.cretu@arm.com>
diff --git a/cmake/FindPlantUML.cmake b/cmake/FindPlantUML.cmake
index ae61be7..c7eeedf 100644
--- a/cmake/FindPlantUML.cmake
+++ b/cmake/FindPlantUML.cmake
@@ -31,6 +31,8 @@
 #   PLANTUML_FOUND          = Was the .jar file found and sucesfuly executed.
 #
 
+include(Common/Utils)
+
 find_package(Java 1.8 COMPONENTS Runtime)
 if(Java_Runtime_FOUND)
 	#Check if the jar file is at the user defined location.