spapr_iommu: Make in-kernel TCE table optional

spapr_iommu: Make in-kernel TCE table optional

POWER KVM supports an KVM_CAP_SPAPR_TCE capability which allows allocating
TCE tables in the host kernel memory and handle H_PUT_TCE requests
targeted to specific LIOBN (logical bus number) right in the host without
switching to QEMU. At the moment this is used for emulated devices only
and the handler only puts TCE to the table. If the in-kernel H_PUT_TCE
handler finds a LIOBN and corresponding table, it will put a TCE to
the table and complete hypercall execution. The user space will not be
notified.

Upcoming VFIO support is going to use the same sPAPRTCETable device class
so KVM_CAP_SPAPR_TCE is going to be used as well. That means that TCE
tables for VFIO are going to be allocated in the host as well.
However VFIO operates with real IOMMU tables and simple copying of
a TCE to the real hardware TCE table will not work as guest physical
to host physical address translation is requited.

So until the host kernel gets VFIO support for H_PUT_TCE, we better not
to register VFIO's TCE in the host.

This adds a place holder for KVM_CAP_SPAPR_TCE_VFIO capability. It is not
in upstream yet and being discussed so now it is always false which means
that in-kernel VFIO acceleration is not supported.

This adds a bool @vfio_accel flag to the sPAPRTCETable device telling
that sPAPRTCETable should not try allocating TCE table in the host kernel
for VFIO. The flag is false now as at the moment there is no VFIO.

This adds an vfio_accel parameter to spapr_tce_new_table(), the semantic
is the same. Since there is only emulated PCI and VIO now, the flag is set
to false. Upcoming VFIO support will set it to true.

This is a preparation patch so no change in behaviour is expected

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Alexander Graf <agraf@suse.de>