Currently, the CPU model driver is not implemented for PowerPC.
Host's CPU information is needed to exposed to guests' XML file some
time.

This patch is to implement the callback functions of CPU model driver.
Signed-off-by: NLi Zhang <zhlcindy@linux.vnet.ibm.com>
Acked-by: NMichal Privoznik <mprivozn@redhat.com>