of/pci: Use of_pci_range_parser

This patch converts the pci_load_of_ranges function to use the new common
of_pci_range_parser.

Signed-off-by: Andrew Murray <amurray@embedded-bits.co.uk>
Signed-off-by: Andrew Murray <Andrew.Murray@arm.com>
Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>