phb4: Disable nodal scoped DMA accesses when PB pump mode is enabled

By default when a PCIe device issues a read request via the PHB it is first
issued with nodal scope. When accessing GPU memory the NPU does not know at the
time of response if the requested memory page is off node or not. Therefore
every read of GPU memory by a PHB is retried with larger scope which introduces
bandwidth and latency issues.

On smaller boxes which have pump mode enabled nodal and group scoped reads are
treated the same and both types of request are broadcast to one chip. Therefore
we can avoid the retry by disabling nodal scope on the PHB for these boxes. On
larger boxes nodal (single chip) and group (multiple chip) scoped reads are
treated differently. Therefore we avoid disabling nodal scope on large boxes
which have pump mode disabled to avoid all PHB requests being broadcast to
multiple chips.

Signed-off-by: Alistair Popple <alistair@popple.id.au>
Signed-off-by: Stewart Smith <stewart@linux.ibm.com>

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