PCI/AER: Expose internal API for obtaining AER information

Export some common AER functions and structures for other PCI core drivers
to use.  Since this is making the function externally visible inside the
PCI core, prepend "aer_" to the function name.

Signed-off-by: Keith Busch <keith.busch@intel.com>
[bhelgaas: move AER declarations from linux/aer.h to drivers/pci/pci.h]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Sinan Kaya <okaya@kernel.org>
Reviewed-by: Oza Pawandeep <poza@codeaurora.org>