dts: mpc512x: prepare for preprocessor support

prepare C preprocessor support when processing MPC512x DTS files
- switch from DTS syntax to CPP syntax for include specs
- create a symlink such that DTS processing can reference includes

Signed-off-by: Gerhard Sittig <gsi@denx.de>
Signed-off-by: Anatolij Gustschin <agust@denx.de>

arch/powerpc/boot/dts/ac14xx.dts

@@ -10,7 +10,7 @@
  */
 
 
-/include/ "mpc5121.dtsi"
+#include <mpc5121.dtsi>
 
 / {
 	model = "ac14xx";

arch/powerpc/boot/dts/include/dt-bindings

@@ -0,0 +1 @@
+../../../../../include/dt-bindings

arch/powerpc/boot/dts/mpc5121ads.dts

@@ -9,7 +9,7 @@
  * option) any later version.
  */
 
-/include/ "mpc5121.dtsi"
+#include <mpc5121.dtsi>
 
 / {
 	model = "mpc5121ads";

arch/powerpc/boot/dts/pdm360ng.dts

@@ -13,7 +13,7 @@
  * option) any later version.
  */
 
-/include/ "mpc5121.dtsi"
+#include <mpc5121.dtsi>
 
 / {
 	model = "pdm360ng";