powerpc/85xx: Add binding for SCFG

SCFG provides SoC specific configuration and status registers for
the chip. Add this for powerpc platform.

Signed-off-by: Wang Dongsheng <[e-mail]>
Signed-off-by: Scott Wood <[e-mail]>

Documentation/devicetree/bindings/powerpc/fsl/scfg.txt

···
+Freescale Supplement configuration unit (SCFG)
+
+SCFG is the supplemental configuration unit, that provides SoC specific
+configuration and status registers for the chip. Such as getting PEX port
+status.
+
+Required properties:
+
+- compatible: should be "fsl,<chip>-scfg"
+- reg: should contain base address and length of SCFG memory-mapped
+registers
+
+Example:
+
+	scfg: global-utilities@fc000 {
+		compatible = "fsl,t1040-scfg";
+		reg = <0xfc000 0x1000>;
+	};