hwc: Fix reserved field usage

Use the top 16 bits of reserved[3] for HDMI
and the bottom 16 for FPS. A follow up patch
in the MDP driver will get rid of reserved field
usage entirely.

Change-Id: Ic9f7a2f91b46b0dec830ea54784b7775009fbe48

libgralloc/framebuffer.cpp

@@ -291,7 +291,7 @@ int mapFrameBufferLocked(struct private_module_t* module)
     float xdpi = (info.xres * 25.4f) / info.width;
     float ydpi = (info.yres * 25.4f) / info.height;
     //The reserved[3] field is used to store FPS by the driver.
-    float fps  = info.reserved[3];
+    float fps  = info.reserved[3] & 0xFF;
 
     ALOGI("using (fd=%d)\n"
           "id           = %s\n"