drm_hwcomposer: Parse and store possible_clones information

drmModeEncoder has a field called possible_clones. It's a bit mask
which tells if the encoder could be simultaneously connected, to the
same CRTC, with the encoders specified in the possible_clones mask.

Signed-off-by: Alexandru Gheorghe <alexandru-cosmin.gheorghe@arm.com>
diff --git a/drmencoder.cpp b/drmencoder.cpp
index 6ae5d9a..277f9a4 100644
--- a/drmencoder.cpp
+++ b/drmencoder.cpp
@@ -39,6 +39,14 @@
   return crtc_;
 }
 
+bool DrmEncoder::CanClone(DrmEncoder *possible_clone) {
+  return possible_clones_.find(possible_clone) != possible_clones_.end();
+}
+
+void DrmEncoder::AddPossibleClone(DrmEncoder *possible_clone) {
+  possible_clones_.insert(possible_clone);
+}
+
 void DrmEncoder::set_crtc(DrmCrtc *crtc) {
   crtc_ = crtc;
   display_ = crtc->display();