powerpc/pseries: Reject discontiguous/non-zero based MSI-X requests

There's no way for us to express to firmware that we want a
discontiguous, or non-zero based, range of MSI-X entries. So we
must reject such requests.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>