The naming of eeh_{add_to|remove_from}_parent_pe() doesn't really reflect
what they actually do. If the PE referred to be edev->pe_config_addr
already exists under that PHB then the edev is added to that PE. However,
if the PE doesn't exist the a new one is created for the edev.

The bulk of the implementation of eeh_add_to_parent_pe() covers that
second case. Similarly, most of eeh_remove_from_parent_pe() is
determining when it's safe to delete a PE.
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200725081231.39076-12-oohall@gmail.com