IBM Power processors differ uniquely across generations (such as power6,
power7, power8). Each generation signifies a new PowerISA version
that exhibits features unique to that generation.
The higher 16 bits of PVR for IBM Power processors encode the CPU
generation, while the CPU chip (sub)version is encoded in lower 16 bits.

For all practical purposes of launching a VM, we care about the
generation which the vCPU will belong to, and not specifically the chip
version. This patch updates the libvirt PVR check to reflect this
relationship. It allows libvirt to select the right CPU generation
in case the exact match for a a specific CPU is not found.
Hence, there will no longer be a need to add each PowerPC CPU model to
cpu_map.xml; just adding entry for the matching ISA generation will
suffice.

It also contains changes to cpu_map.xml since processor generations
as understood by QEMU compat mode go as "power6", "power7" or "power8"
[Reference : QEMU commit 8dfa3a5e85 ]
Signed-off-by: NPrerna Saxena <prerna@linux.vnet.ibm.com>
Signed-off-by: NPradipta Kr. Banerjee <bpradip@in.ibm.com>
Signed-off-by: NAnton Blanchard <anton@samba.org>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>