Fix 16bit boot animation

The implementation of the 16 bit boot animation has changed.
Now we need TARGET_BOOTANIMATION_USE_RGB565 := true
See:
https://github.com/CyanogenMod/android_frameworks_base/blob/cm-11.0/cmds/bootanimation/Android.mk#L37

Change-Id: I8d1e3d4dbe9bcd92d6dbea5921019f888c085c90