of/pci: Provide support for parsing PCI DT ranges property

This patch factors out common implementation patterns to reduce overall kernel
code and provide a means for host bridge drivers to directly obtain struct
resources from the DT's ranges property without relying on architecture specific
DT handling. This will make it easier to write archiecture independent host bridge
drivers and mitigate against further duplication of DT parsing code.

This patch can be used in the following way:

	struct of_pci_range_parser parser;
	struct of_pci_range range;

	if (of_pci_range_parser_init(&parser, np))
		; //no ranges property

	for_each_of_pci_range(&parser, &range) {

		/*
			directly access properties of the address range, e.g.:
			range.pci_space, range.pci_addr, range.cpu_addr,
			range.size, range.flags

			alternatively obtain a struct resource, e.g.:
			struct resource res;
			of_pci_range_to_resource(&range, np, &res);
		*/
	}

Additionally the implementation takes care of adjacent ranges and merges them
into a single range (as was the case with powerpc and microblaze).

Signed-off-by: Andrew Murray <Andrew.Murray@arm.com>
Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Rob Herring <rob.herring@calxeda.com>
Tested-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>