powerpc/powernv: Don't map M64 segments using M32DT

If M64 has been supported, the prefetchable 64-bits memory resources
shouldn't be mapped to the corresponding PE# via M32DT. Unfortunately,
we're doing that in pnv_ioda_setup_pe_seg() wrongly. The issue was
introduced by commit 262af557 ("powerpc/powernv: Enable M64 aperatus
for PHB3"). The patch fixes the issue by simply skipping M64 resources
when updating to M32DT.

Cc: <stable@vger.kernel.org>  # v3.17+
Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>