PCI/ERR: Recover from RCiEP AER errors

PCI/ERR: Recover from RCiEP AER errors

Add support for handling AER errors detected by Root Complex Integrated
Endpoints (RCiEPs).  These errors are signaled to software natively via a
Root Complex Event Collector (RCEC) or non-natively via ACPI APEI if the
platform retains control of AER or uses a non-standard RCEC-like device.

When recovering from RCiEP errors, the Root Error Command and Status
registers are in the AER Capability of an associated RCEC (if any), not in
a Root Port.  In the non-native case, the platform is responsible for those
registers and we can't touch them.

[bhelgaas: commit log, etc]
Co-developed-by: Sean V Kelley <sean.v.kelley@intel.com>
Link: https://lore.kernel.org/r/20201121001036.8560-13-sean.v.kelley@intel.com
Signed-off-by: Sean V Kelley <sean.v.kelley@intel.com>
Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>