build: use GNUInstallDirs where possible

Some installation destinations were already converted to the
GNUInstallDirs standard in e3cf4d0cf. This patch converts the share and
include directories (typically /usr/share and /usr/include respectively)
as well.

Type: improvement
Change-Id: Id481b16604f3f52203166a5c0647f43d6eb05239
Signed-off-by: Wim de With <wf@dewith.io>
diff --git a/src/cmake/plugin.cmake b/src/cmake/plugin.cmake
index df96aa8..f971e5f 100644
--- a/src/cmake/plugin.cmake
+++ b/src/cmake/plugin.cmake
@@ -44,7 +44,7 @@
       ${CMAKE_CURRENT_BINARY_DIR}/${f}.h
       ${CMAKE_CURRENT_BINARY_DIR}/${f}_enum.h
       ${CMAKE_CURRENT_BINARY_DIR}/${f}_types.h
-      DESTINATION include/vpp_plugins/${name}/${dir}
+      DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/vpp_plugins/${name}/${dir}
       COMPONENT ${PLUGIN_DEV_COMPONENT}
     )
   endforeach()
@@ -86,7 +86,7 @@
       get_filename_component(dir ${file} DIRECTORY)
       install(
 	FILES ${file}
-	DESTINATION include/vpp_plugins/${name}/${dir}
+	DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/vpp_plugins/${name}/${dir}
 	COMPONENT vpp-dev
       )
     endforeach()