target/ppc/spapr: Enable mitigations by default for pseries-4.0 machine type

target/ppc/spapr: Enable mitigations by default for pseries-4.0 machine type

There are currently 3 mitigations the availability of which is controlled
by the spapr-caps mechanism, cap-cfpc, cap-sbbc, and cap-ibs. Enable these
mitigations by default for the pseries-4.0 machine type.

By now machine firmware should have been upgraded to allow these
settings.

Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Message-Id: <20190301044609.9626-3-sjitindarsingh@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>