Overlays are currently enabled and disabled with a boolean in the struct
omap_overlay_info. The overlay info is set with ovl->set_overlay_info(),
and made into use with mgr->apply().

This doesn't work properly, as the enable/disable status may affect also
other overlays, for example when using fifo-merge. Thus the enabling and
disabling of the overlay needs to be done outside the normal overlay
configuration.

This patch achieves that by doing the following things:

1) Add function pointers to struct omap_overlay: enable(), disable() and
is_enabled(). These are used to do the obvious. The functions may block.

2) Move the "enabled" field from struct omap_overlay to ovl_priv_data.

3) Add a new route for settings to be applied to the HW, called
"extra_info". The status of the normal info and extra_info are tracked
separately.

The point here is to allow the normal info to be changed and
applied in non-blocking matter, whereas the extra_info can only be
changed when holding the mutex. This makes it possible to, for example,
set the overlay enable flag, apply it, and wait until the HW has taken
the flag into use.

This is not possible if the enable flag would be in the normal info, as
a new value for the flag could be set at any time from the users of
omapdss.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>