powerpc/eeh: Kill off eeh_ops->get_pe_addr()

This is used in precisely one place which is in pseries specific platform
code.  There's no need to have the callback in eeh_ops since the platform
chooses the EEH PE addresses anyway. The PowerNV implementation has always
been a stub too so remove it.

Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200725081231.39076-5-oohall@gmail.com