Representing flash partitions in devicetree

In addition to the upstream binding, another property is added:

Optional properties:
- partuuid : The partition UUID for this partition.

Additionally, barebox also supports partitioning the eMMC boot partitions if
the partition table node is named appropriately:
- partitions : user partition
- boot0-partitions : boot0 partition
- boot1-partitions : boot1 partition

Examples:

flash@0 {
	partitions {
		compatible = "fixed-partitions";
		#address-cells = <1>;
		#size-cells = <1>;

		state_part: state {
			partuuid = "16367da7-c518-499f-9aad-e1f366692365";
		};
	};
};

emmc@1 {
	boot0-partitions {
		compatible = "fixed-partitions";
		#address-cells = <1>;
		#size-cells = <1>;

		barebox@0 {
			label = "barebox";
			reg = <0x0 0x300000>;
		};
	};
};