ARM: bcm281xx: Add DT support for SMC handler

- Adds devicetree binding and documentation for the smc handler

Updates from V1:
- Created this separate patch for the DT portion
- Added SoC compatible to smc binding
Signed-off-by: Christian Daudt <csd@broadcom.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>

Documentation/devicetree/bindings/misc/smc.txt

+Broadcom Secure Monitor Bounce buffer
+-----------------------------------------------------
+This binding defines the location of the bounce buffer
+used for non-secure to secure communications.
+
+Required properties:
+- compatible : "bcm,kona-smc"
+- reg : Location and size of bounce buffer
+
+Example:
+	smc@0x3404c000 {
+		compatible = "bcm,bcm11351-smc", "bcm,kona-smc";
+		reg = <0x3404c000 0x400>; //1 KiB in SRAM
+	};

arch/arm/boot/dts/bcm11351.dtsi

@@ -31,6 +31,11 @@ gic: interrupt-controller@3ff00100 {
 		      <0x3ff00100 0x100>;
 	};
 
+	smc@0x3404c000 {
+		compatible = "bcm,bcm11351-smc", "bcm,kona-smc";
+		reg = <0x3404c000 0x400>; //1 KiB in SRAM
+	};
+
 	uart@3e000000 {
 		compatible = "bcm,bcm11351-dw-apb-uart", "snps,dw-apb-uart";
 		status = "disabled";