selftests/powerpc: Add VF recovery tests

The basic EEH test ignores VFs since we the way the eeh_dev_break debugfs
interface works means that if multiple VFs are enabled we may cause errors
on all them them. However, we can work around that by only enabling a
single VF at a time.

This patch adds some infrastructure for finding SR-IOV capable devices and
enabling / disabling VFs so we can exercise the VF specific EEH recovery
paths. Two new tests are added, one for testing EEH aware devices and one
for EEH un-aware VFs.

Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201103044503.917128-3-oohall@gmail.com