hwc: Add support for external-only layers

Add support for different types of external-only layers
EXTERNAL_ONLY: General purpose
EXTERNAL_BLOCK: Blocks the display of other ext-only layers
EXTERNAL_CC: Used for closed captions with videos.

Change-Id: I9cc7b9a1dbf1085194725474d6a4d1094e27a0c8
Acked-by: Saurabh Shah <saurshah@codeaurora.org>
diff --git a/libgralloc/alloc_controller.cpp b/libgralloc/alloc_controller.cpp
index 97255ba..e4d1d68 100644
--- a/libgralloc/alloc_controller.cpp
+++ b/libgralloc/alloc_controller.cpp
@@ -57,7 +57,7 @@
     if(usage & (GRALLOC_HEAP_MASK | GRALLOC_USAGE_PROTECTED |
                 GRALLOC_USAGE_PRIVATE_CP_BUFFER))
         return false;
-    if(usage & (GRALLOC_HEAP_MASK | GRALLOC_USAGE_EXTERNAL_ONLY))
+    if(usage & (GRALLOC_HEAP_MASK | GRALLOC_USAGE_PRIVATE_EXTERNAL_ONLY))
         return false;
     //Return true by default
     return true;