Overlay support for legacy camera libs

1. Rename OverlayHtc to Overlay in file names
2. Use BOARD_USES_LEGACY_OVERLAY to enable
Credits to Arne Coucheron
Signed-off-by: Jan Jasper de Kroon <jajadekroon@gmail.com>

Change-Id: I17e82f16720828d0858822d3f5aa449b0859503f