of/address: Add support for 3 address cell bus

of/address: Add support for 3 address cell bus

There's a few custom bus bindings (e.g. fsl,qoriq-mc) which use a
3 cell format with custom flags in the high cell. We can match these
buses as a fallback if we didn't match on PCI bus which is the only
standard bus binding with 3 address cells.

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Rob Herring <[email protected]>