powerpc/powernv/ioda1: Remove dead code for a single device PE

At the moment PNV_IODA_PE_DEV is only used for NPU PEs which are not
present on IODA1 machines (i.e. POWER7) so let's remove a piece of
dead code.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Sam Bobroff <sbobroff@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>