PCI: Convert pci_resource_to_user() to a weak function

Convert pci_resource_to_user() to a weak function so the existing
architecture-specific implementations will automatically override the
generic one.  This allows us to remove HAVE_ARCH_PCI_RESOURCE_TO_USER
definitions and avoid the conditional compilation for this single function.

Link: https://lore.kernel.org/r/20190729101401.28068-1-efremov@linux.com
Link: https://lore.kernel.org/r/20190729101401.28068-2-efremov@linux.com
Link: https://lore.kernel.org/r/20190729101401.28068-3-efremov@linux.com
Link: https://lore.kernel.org/r/20190729101401.28068-4-efremov@linux.com
Link: https://lore.kernel.org/r/20190729101401.28068-5-efremov@linux.com
Link: https://lore.kernel.org/r/20190729101401.28068-6-efremov@linux.com


Signed-off-by: Denis Efremov <efremov@linux.com>
[bhelgaas: squash into one commit]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Paul Burton <paul.burton@mips.com>	# MIPS