powerpc/powernv/pci-ioda: fix kdump with non-power-of-2 crashkernel=

The 32-bit TCE table initialization relies on the DMA window having a
size equal to a power of 2 (and checks for it explicitly). But
crashkernel= has no constraint that requires a power-of-2 be specified.
This causes the kdump kernel to fail to boot as none of the PCI devices
(including the disk controller) are successfully initialized.

After this change, the PCI devices successfully set up the 32-bit TCE
table and kdump succeeds.

Fixes: aca6913f ("powerpc/powernv/ioda2: Introduce helpers to allocate TCE pages")
Signed-off-by: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>
Cc: stable@vger.kernel.org # 4.2
Tested-by: Jan Stancek <jstancek@redhat.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>