powerpc/eeh: Clean up and document event handling functions

Remove unnecessary tags in eeh_handle_normal_event(), and add function
comments for eeh_handle_normal_event() and eeh_handle_special_event().

The only functional difference is that in the case of a PE reaching the
maximum number of failures, rather than one message telling you of this
and suggesting you reseat the device, there are two separate messages.

Suggested-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Russell Currey <ruscur@russell.cc>
Reviewed-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Reviewed-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>