Add PPC cpu driver.

Add PPC cpu driver.

To add support for running libvirt on PowerPC, a CPU driver for the
PowerPC platform must be added.
Most generic cpu driver routines such as CPU compare, decode, etc
are based on CPUID comparison and are not relevant for non-x86
platforms.
Here, we introduce stubs for relevant PowerPC routines invoked by libvirt.

Signed-off-by: Prerna Saxena <prerna@linux.vnet.ibm.com>
Signed-off-by: Anton Blanchard <anton@au.ibm.com>