brcm63xx: make use of dt-includes

Now that we have a dtc command that invokes the preprocessor, make use
of it and replace the magic numbers with KEY_* defines.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>

SVN-Revision: 46391

target/linux/brcm63xx/dts/usr9108.dts

@@ -1,6 +1,8 @@
 /dts-v1/;
 
-/include/ "bcm6348.dtsi"
+#include "bcm6348.dtsi"
+
+#include <dt-bindings/input/input.h>
 
 / {
 	model = "USRobotics 9108";