power: Add support for camera preview in powerHAL

Change adds support for camera hint detection
in powerHAL.

Change-Id: Iae9bdcfe61ca65cf18a4c1a61dbcdd0f67285d8b
diff --git a/include/hardware/power.h b/include/hardware/power.h
index af7799e..084cba8 100644
--- a/include/hardware/power.h
+++ b/include/hardware/power.h
@@ -46,7 +46,8 @@
      */
     POWER_HINT_VIDEO_ENCODE = 0x00000003,
     POWER_HINT_VIDEO_DECODE = 0x00000004,
-    POWER_HINT_LOW_POWER = 0x00000005
+    POWER_HINT_LOW_POWER = 0x00000005,
+    POWER_HINT_CAM_PREVIEW = 0x00000006
 } power_hint_t;
 
 typedef enum {