powerpc/eeh: Make EEH driver device hotplug safe

In the Linux kernel, the following vulnerability has been resolved: powerpc/eeh: Make EEH driver device hotplug safe Multiple race conditions existed between the PCIe hotplug driver and the EEH driver, leading to a variety of kernel oopses of the same general nature: <pcie device unplug> <eeh driver trigger> <hotplug removal trigger> <pcie tree reconfiguration> <eeh recovery next step> <oops in EEH driver bus iteration loop> A second class of oops is also seen when the underlying bus disappears during device recovery. Refactor the EEH module to be PCI rescan and remove safe. Also clean up a few minor formatting / readability issues.