iommu/of: make of_pci_map_rid() available for other devices too

iommu-map property is also used by devices with fsl-mc. This
patch moves the of_pci_map_rid to generic location, so that it
can be used by other busses too.

'of_pci_map_rid' is renamed here to 'of_map_rid' and there is no
functional change done in the API.

Signed-off-by: Nipun Gupta <nipun.gupta@nxp.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>