Revert "OMAPDSS: APPLY: add fifo merge support funcs"

This reverts commit fb011974.

Adding fifo merge feature as an omapdss internal configuration was a
mistake. We cannot hide from the users of omapdss the complexities of
fifo merge.

The previous commit removed fifo merge itself, and this removes the
remaining fifo merge support functions.

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