powerpc/powernv: Add PCI error injection debugfs entry

The patch adds debugfs file (/sys/kernel/debug/powerpc/PCIxxxx/
err_injct), which accepts following formated string, to support
error injection. It will be used to support userland utility
"errinjct" in future.

  "pe_no:0:function:address:mask" - 32-bits PCI errors
  "pe_no:1:function:address:mask" - 64-bits PCI errors

Signed-off-by: Mike Qiu <qiudayu@linux.vnet.ibm.com>
Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>