gralloc: Add a private flag for INTERNAL only

Add PRIV_FLAGS_INTERNAL_ONLY which will be used by clients
to know if that is an INTERNAL only layer.

Change-Id: I2cc69bcbc86c18d97ce0c841670b760e48721ffa
diff --git a/libgralloc/gralloc_priv.h b/libgralloc/gralloc_priv.h
index 2601953..02db068 100755
--- a/libgralloc/gralloc_priv.h
+++ b/libgralloc/gralloc_priv.h
@@ -172,6 +172,7 @@
             PRIV_FLAGS_USES_ION           = 0x00000008,
             PRIV_FLAGS_USES_ASHMEM        = 0x00000010,
             PRIV_FLAGS_NEEDS_FLUSH        = 0x00000020,
+            PRIV_FLAGS_INTERNAL_ONLY      = 0x00000040,
             PRIV_FLAGS_NON_CPU_WRITER     = 0x00000080,
             PRIV_FLAGS_NONCONTIGUOUS_MEM  = 0x00000100,
             PRIV_FLAGS_CACHED             = 0x00000200,