of: Merge of_get_address() and of_get_pci_address() implementations

of_get_address() and of_get_pci_address() are the same implementation
except of_get_pci_address() takes the PCI BAR number rather than an
index. Modify the of_get_address() implementation to work on either
index or BAR and provide wrapper functions for the existing functions.

Cc: Frank Rowand <frowand.list@gmail.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210527194547.1287934-3-robh@kernel.org