metag: *.dts: include using preprocessor

Include *.dtsi files from *.dts using the preprocessor to set a good
example for future device tree files. Files included in the old way
don't get pre-processed.

Signed-off-by: James Hogan <[e-mail]>
Acked-by: Grant Likely <[e-mail]>
Cc: [e-mail]

arch/metag/boot/dts/skeleton.dts

···
  */
 /dts-v1/;
 
-/include/ "skeleton.dtsi"
+#include "skeleton.dtsi"

arch/metag/boot/dts/tz1090.dtsi

···
  * published by the Free Software Foundation.
  */
 
-/include/ "skeleton.dtsi"
+#include "skeleton.dtsi"
 
 / {
 	compatible = "toumaz,tz1090", "img,meta";

arch/metag/boot/dts/tz1090_generic.dts

···
  */
 /dts-v1/;
 
-/include/ "tz1090.dtsi"
+#include "tz1090.dtsi"