sdm: Add property to enable destination scalar during bootup.

Add property sdm.mixer_resolution to configure the layer mixer
resolution during boot up and switch back to requested mixer
resolution when a layer with higher resolution disappears.

Change-Id: I99f12d5f1a858daa41e41be1ff81833adbe3c651
CRs-Fixed: 1038976

sdm/include/utils/debug.h

@@ -77,6 +77,7 @@ class Debug {
   static bool IsUbwcTiledFrameBuffer();
   static bool IsAVRDisabled();
   static bool IsExtAnimDisabled();
+  static DisplayError GetMixerResolution(uint32_t *width, uint32_t *height);
   static bool GetProperty(const char *property_name, char *value);
   static bool SetProperty(const char *property_name, const char *value);