of: address: Use IS_ENABLED() for !CONFIG_PCI

Convert address.c to use IS_ENABLED() instead of ifdefs for the
public PCI functions. This simplifies the ifdefs in of_address.h.

Cc: Frank Rowand <frowand.list@gmail.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210527194547.1287934-4-robh@kernel.org