pseries: Add device tree properties for VMX/VSX and DFP under kvm

Sufficiently recent PAPR specifications define properties "ibm,vmx"
and "ibm,dfp" on the CPU node which advertise whether the VMX vector
extensions (or the later VSX version) and/or the Decimal Floating
Point operations from IBM's recent POWER CPUs are available.

Currently we do not put these in the guest device tree and the guest
kernel will consequently assume they are not available.  This is good,
because they are not supported under TCG.  VMX is similar enough to
Altivec that it might be trivial to support, but VSX and DFP would
both require significant work to support in TCG.

However, when running under kvm on a host which supports these
instructions, there's no reason not to let the guest use them.  This
patch, therefore, checks for the relevant support on the host CPU
and, if present, advertises them to the guest as well.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>
