OMAPDSS: APPLY: add dss_setup_fifos

Currently fifo threshold configuration is done per overlay or per
manager. However, when a fifo size configuration is added, we need to
always configure the thresholds for all overlays.

This patch prepares for that by changing the fifo threshold
configuration to always handle all overlays.

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