PCI: Move OF-related PCI functions into PCI core

Following what has been done for other subsystems, move the remaining PCI
related code out of drivers/of/ and into drivers/pci/of.c

With this, we can kill a few kconfig symbols.

Signed-off-by: Rob Herring <robh@kernel.org>
[bhelgaas: minor whitespace, comment cleanups]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Frank Rowand <frowand.list@gmail.com>