Power: add back support for camera preview in power HAL

This commit basically reverts commit fcd7a60ea7717a8a02ff9220bf080bb1583379ce
and updates the code after POWER_HINT_AUDIO removal
diff --git a/include/hardware/power.h b/include/hardware/power.h
index 70bc745..5a6e849 100644
--- a/include/hardware/power.h
+++ b/include/hardware/power.h
@@ -71,6 +71,7 @@
     POWER_HINT_CPU_BOOST    = 0x00000110,
     POWER_HINT_LAUNCH_BOOST = 0x00000111,
     POWER_HINT_SET_PROFILE  = 0x00000112,
+    POWER_HINT_CAM_PREVIEW  = 0x00000113
 } power_hint_t;
 
 typedef enum {