drm_hwcomposer: Tracking of the DRM FB objects using RAII

DRM framebuffer objects must be kept registered in DRM/KMS
while used for scanning-out (After atomic commit applied
for processing by display controller and until next atomic
commit is applied for processing).

Existing logic for tracking current state is overcomplicated and
needs to be redesigned. Also further developing of drm_hwc will
require migration to asynchronous atomic commit, so additional
asynchronous FB cleanup logic must be created.
Buffer caching logic will also benefit from this.

With the RAII all further changes will be less painful and more robust.

By this commit I also renamed DrmGenericImporter to DrmFbImporter:
'Fb' word is present in most of existing composers (android and linux)
so it will be easier to compare different implementations.

Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>
diff --git a/DrmHwcTwo.h b/DrmHwcTwo.h
index a0d8cdd..b4e1ce8 100644
--- a/DrmHwcTwo.h
+++ b/DrmHwcTwo.h
@@ -25,7 +25,6 @@
 
 #include "compositor/DrmDisplayCompositor.h"
 #include "compositor/Planner.h"
-#include "drm/DrmGenericImporter.h"
 #include "drm/ResourceManager.h"
 #include "drm/VSyncWorker.h"
 #include "drmhwcomposer.h"
@@ -164,8 +163,7 @@
   class HwcDisplay {
    public:
     HwcDisplay(ResourceManager *resource_manager, DrmDevice *drm,
-               std::shared_ptr<Importer> importer, hwc2_display_t handle,
-               HWC2::DisplayType type);
+               hwc2_display_t handle, HWC2::DisplayType type);
     HwcDisplay(const HwcDisplay &) = delete;
     HWC2::Error Init(std::vector<DrmPlane *> *planes);
 
@@ -305,10 +303,6 @@
       return connector_;
     }
 
-    const std::shared_ptr<Importer> &importer() const {
-      return importer_;
-    }
-
     ResourceManager *resource_manager() const {
       return resource_manager_;
     }
@@ -329,7 +323,6 @@
     ResourceManager *resource_manager_;
     DrmDevice *drm_;
     DrmDisplayCompositor compositor_;
-    std::shared_ptr<Importer> importer_;
     std::unique_ptr<Planner> planner_;
 
     std::vector<DrmPlane *> primary_planes_;