mtd: partitions: Add AFS partitions DT bindings

This adds device tree bindings for ARM Firmware Suite
flash partitioning used in NOR flashes on ARM reference
designs.

Cc: [e-mail]
Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>
Signed-off-by: Richard Weinberger <[e-mail]>

Documentation/devicetree/bindings/mtd/partitions/arm,arm-firmware-suite.txt

···
+ARM AFS - ARM Firmware Suite Partitions
+=======================================
+
+The ARM Firmware Suite is a flash partitioning system found on the
+ARM reference designs: Integrator AP, Integrator CP, Versatile AB,
+Versatile PB, the RealView family, Versatile Express and Juno.
+
+Required properties:
+- compatible : (required) must be "arm,arm-firmware-suite"
+
+Example:
+
+flash@0 {
+	partitions {
+		compatible = "arm,arm-firmware-suite";
+	};
+};