cmake: Clean up CMakeLists.txt for QPA plugin

plugins/qpa/CMakeLists.txt

-include_directories(${Qt5Core_PRIVATE_INCLUDE_DIRS})
-include_directories(${Qt5Gui_PRIVATE_INCLUDE_DIRS})
-
 set(QPA_SOURCES
     backingstore.cpp
     eglhelpers.cpp
@@ -19,15 +16,16 @@ ecm_qt_declare_logging_category(QPA_SOURCES HEADER logging.h IDENTIFIER KWIN_QPA
 add_library(KWinQpaPlugin OBJECT ${QPA_SOURCES})
 target_compile_definitions(KWinQpaPlugin PRIVATE QT_STATICPLUGIN)
 
-set(QT5PLATFORMSUPPORT_LIBS
+target_include_directories(KWinQpaPlugin PRIVATE
+    ${Qt5Core_PRIVATE_INCLUDE_DIRS}
+    ${Qt5Gui_PRIVATE_INCLUDE_DIRS}
+)
+
+target_link_libraries(KWinQpaPlugin PRIVATE
     Qt5::FontDatabaseSupportPrivate
     Qt5::ThemeSupportPrivate
     Qt5::EventDispatcherSupportPrivate
-)
-
-target_link_libraries(KWinQpaPlugin
-    ${QT5PLATFORMSUPPORT_LIBS}
-    ${FREETYPE_LIBRARIES} # Must be after QT5PLATFORMSUPPORT_LIBS
+    Freetype::Freetype # Must be after Qt5 platform support libs
     Fontconfig::Fontconfig
     kwin
 )