Don't force GPU composite for older devices

Older devices (8960) don't take this very well in programs like
Netflix. Modeled on 94b8632b85e2b6588a1b3260d1f4e48462501d4b

Change-Id: Ie716bbfb6f6560d8f9f52b7b72ca0b04d1bad6b8
liboverlay: do not return error if fb num >= 2 doesn't exist (writeback).

Some devices doesn't have writeback support, but needs HDMI (fb1)
This will allow them not to break HDMI support.
This is a cleaner implementation as it won't change handling on
8660 devices having writeback (if those exists).

Change-Id: I6c09759dfa4f2b1734f85012cab4eb4f350820ea
libcopybit: Add missing return statement

Change-Id: I662699b7418eba2c4792ed6c7c7b628762ebe03b
(cherry picked from commit f2e940109252c63b6e21f929e45ba794dfe12b95)
copybit: Fix type conversion error for GCC 4.7

    GCC 4.7 has stricter type conversion rules in copybit.cpp

Change-Id: I7f8572e2d9416ccb2ba17e707c7f75a2e69d69cf