drm_hwcomposer: Move eglCreateImageKHR into Importer

Since NV has a "special" nonstandard way to get an EGLImage from a
handle, move this into Importer where the other NV specialness is
abstracted.  For the platformdrmgeneric case, use the dmabuf EGL
Extension.

Change-Id: I5353f4c95f55174df55ba92931cdc9a9eab80dca
Signed-off-by: Robert Foss <robert.foss@collabora.com>
diff --git a/platform.h b/platform.h
index 70e5e81..e417bf7 100644
--- a/platform.h
+++ b/platform.h
@@ -38,6 +38,10 @@
   // Creates a platform-specific importer instance
   static Importer *CreateInstance(DrmResources *drm);
 
+  // Imports EGLImage for glcompositor, since NV handles this in non-standard
+  // way, and fishing out the details is specific to the gralloc used.
+  virtual EGLImageKHR ImportImage(EGLDisplay egl_display, buffer_handle_t handle) = 0;
+
   // Imports the buffer referred to by handle into bo.
   //
   // Note: This can be called from a different thread than ReleaseBuffer. The