cpu: Add removedPolicy parameter to virCPUUpdate

cpu: Add removedPolicy parameter to virCPUUpdate

virCPUUpdate check the CPU definition for features that were marked as
removed in the specified CPU model and explicitly adds those that were
not mentioned in the definition. So far such features were added with
VIR_CPU_FEATURE_DISABLE policy, but the caller may want to use a
different policy in some situations, which is now possible via the
removedPolicy parameter.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>