powerpc/powernv: Build DMA space for PE on PHB3

The patch intends to build 32-bits DMA space for individual PEs on
PHB3. The TVE# is recognized by the combo of PE# and fixed bits
from DMA address, which is zero for 32-bits DMA space.

Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>