PCI: OF: Add generic function to parse and allocate PCI resources

The patch moves the gen_pci_parse_request_of_pci_ranges() function from
drivers/pci/host/pci-host-common.c into drivers/pci/of.c to easily share
common source code between PCI host drivers.

Signed-off-by: Cyrille Pitchen <cyrille.pitchen@free-electrons.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>