spapr_pci: Remove unhelpful pagesize warning

spapr_pci: Remove unhelpful pagesize warning

By default, the IOMMU model built into the spapr virtual PCI host bridge
supports 4kiB and 64kiB IOMMU page sizes.  However this can be overridden
which may be desirable to allow larger IOMMU page sizes when running a
guest with hugepage backing and passthrough devices.  For that reason a
warning was printed when the device wasn't configured to allow the pagesize
with which guest RAM is backed.

Experience has proven, however, that this message is more confusing than
useful.  Worse it sometimes makes little sense when the host-available page
sizes don't match those available on the guest, which can happen with
a POWER8 guest running on a POWER9 KVM host.

Long term we do want better handling to allow large IOMMU page sizes to be
used, but for now this parameter and warning don't really accomplish it.
So, remove the message, pending a better solution.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>