cpu: Use virDomainCapsCPUModelsPtr in cpu driver APIs

cpu: Use virDomainCapsCPUModelsPtr in cpu driver APIs

All APIs which expect a list of CPU models supported by hypervisors were
switched from char **models and int models to just accept a pointer to
virDomainCapsCPUModels object stored in domain capabilities. This avoids
the need to transform virDomainCapsCPUModelsPtr into a NULL-terminated
list of model names and also allows the various cpu driver APIs to
access additional details (such as its usability) about each CPU model.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>