display: Use GRALLOC_USAGE_PROTECTED to indicate secure content

For secure content, use GRALLOC_USAGE_PROTECTED flag instead of
the obsolete flag GRALLOC_USAGE_PRIVATE_CP_BUFFER.

Change-Id: I69bf8cfd3a978fd472608beb44056e1bf55c1414
diff --git a/libgralloc/gpu.cpp b/libgralloc/gpu.cpp
index 0d070f0..291f564 100644
--- a/libgralloc/gpu.cpp
+++ b/libgralloc/gpu.cpp
@@ -252,8 +252,7 @@
     // All buffers marked as protected or for external
     // display need to go to overlay
     if ((usage & GRALLOC_USAGE_EXTERNAL_DISP) ||
-        (usage & GRALLOC_USAGE_PROTECTED) ||
-        (usage & GRALLOC_USAGE_PRIVATE_CP_BUFFER)) {
+        (usage & GRALLOC_USAGE_PROTECTED)) {
         bufferType = BUFFER_TYPE_VIDEO;
     }