PCI: Use a weak symbol for the empty version of pcibios_add_platform_entries()

I'm not sure if this is going to fly, weak symbols work on the compilers I'm
using, but whether they work for all of the affected architectures I can't say.
I've cc'ed as many arch maintainers/lists as I could find.

But assuming they do, we can use a weak empty definition of
pcibios_add_platform_entries() to avoid having an empty definition on every
arch.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/pci/pci-sysfs.c

@@ -600,6 +600,11 @@ static struct bin_attribute pcie_config_attr = {
 	.write = pci_write_config,
 };
 
+void __attribute__ ((weak)) pcibios_add_platform_entries(struct pci_dev *dev)
+{
+	return;
+}
+
 int __must_check pci_create_sysfs_dev_files (struct pci_dev *pdev)
 {
 	struct bin_attribute *rom_attr = NULL;