OMAPDSS: separate FIFO threshold setup from ovl_setup

OMAPDSS: separate FIFO threshold setup from ovl_setup

Overlay FIFO thresholds are configured with ovl_setup, with all the
other overlay attributes. This patch separates FIFO threshold setup so
that we can later configure FIFO thresholds only when needed.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>