display: Use ion cookie in GPU Tonemapper

- The fd's used for book-keeping can change when the clients
  close and reopen sessions, hence they are not reliable and
  can lead to incorrect virtual address usage causing
  corruption or stale data.
- Hence use ion cookie for book-keeping which is unique for a
  given memory fd.
- Use LRU method free up/reuse on reaching max limit.
- Remove Tonemapper_destroy which is not needed anymore.

Change-Id: I5777649b34210977c18ce20c65e0aa2baa8e7d26
Crs-fixed: 1110175

gpu_tonemapper/TonemapFactory.cpp

@@ -32,9 +32,3 @@ Tonemapper *TonemapperFactory_GetInstance(int type, void *colorMap, int colorMap
 
   return tonemapper;
 }
-
-//------------------------------------------
-void TonemapperFactory_Destroy()
-//------------------------------------------
-{
-}