ARM: Kirkwood: Update PCI-E fixup

ARM: Kirkwood: Update PCI-E fixup

commit 1dc831bf53fddcc6443f74a39e72db5bcea4f15d upstream.

- The code relies on rc_pci_fixup being called, which only happens
  when CONFIG_PCI_QUIRKS is enabled, so add that to Kconfig. Omitting
  this causes a booting failure with a non-obvious cause.
- Update rc_pci_fixup to set the class properly, copying the
  more modern style from other places
- Correct the rc_pci_fixup comment

Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>