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.h b/drmencoder.h
index aeab5ac..c99c36e 100644
--- a/drmencoder.h
+++ b/drmencoder.h
@@ -19,6 +19,7 @@
 
 #include "drmcrtc.h"
 
+#include <set>
 #include <stdint.h>
 #include <vector>
 #include <xf86drmMode.h>
@@ -42,6 +43,8 @@
   const std::vector<DrmCrtc *> &possible_crtcs() const {
     return possible_crtcs_;
   }
+  bool CanClone(DrmEncoder *encoder);
+  void AddPossibleClone(DrmEncoder *possible_clone);
 
  private:
   uint32_t id_;
@@ -49,6 +52,7 @@
   int display_;
 
   std::vector<DrmCrtc *> possible_crtcs_;
+  std::set<DrmEncoder *> possible_clones_;
 };
 }