PCI/AER: Don't select CONFIG_PCIEAER by default

PCIe Advanced Error Reporting (AER) is optional and there's no need for it
to be selected by default.

Remove the "default y" for CONFIG_PCIEAER.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Cc: Russell Currey <ruscur@russell.cc>
Cc: Sam Bobroff <sbobroff@linux.ibm.com>
Cc: Oliver O'Halloran <oohall@gmail.com>