Create separate variables for these components, they are
used in many boards but not all.  This allows finer-grain
selection of the included code with default-configs/*.mak.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20190202072456.6468-27-yang.zhong@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>