OMAPDSS: move omap_dispc_wait_for_irq_interruptible_timeout to dispc-compat.c

We have two functions to wait for a dispc interrupt:

int omap_dispc_wait_for_irq_timeout(u32 irqmask, unsigned long timeout);
int omap_dispc_wait_for_irq_interruptible_timeout(u32 irqmask,

Of these, the former is not used at all, and can be removed. The latter
is only used by the compat layer, and can be moved to the compat layer
code.

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