powerpc/eeh: Remove class code field from edev

The edev->class_code field is never referenced anywhere except for the
platform specific probe functions. The same information is available in
the pci_dev for PowerNV and in the pci_dn on pseries so we can remove
the field.

Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200725081231.39076-11-oohall@gmail.com