An overlay's channel out field isn't a shadow register. The TRM says that it's
taken into effect immediately. This understanding was missing and channel out
was treated as a shadow parameter, and in overlay's private data as extra info.

Program channel out bits directly in dss_ovl_set_manager(). In order to do this
safely, we need to be totally sure that the overlay is disabled in hardware. For
auto update managers, we can assume that the overlay was truly disabled at
dss_ovl_unset_manager() through the wait_pending_extra_info_updates() call.
However, when unsetting manager for an overlay that was previously connected to
a manager in manual update, we can't be sure if the overlay is truly disabled.
That is, op->enabled might not reflect the actual state of the overlay in
hardware. The older manager may require a manual update transfer to truly
disable the overlay. We expect the user of OMAPDSS to take care of this, in
OMAPDSS, we make sure that an overlay's manager isn't unset if there if
extra_info is still dirty for that overlay.

The wrong understanding of channel out bits also explains the reason why we see
sync lost when changing an overlay's manager which was previously connected to a
manual update manager. The following sequence of events caused this:

- When we disable the overlay, no register writes are actually done since the
  manager is manual update, op->enabled is set to false, and the
  extra_info_dirty flag is set. However, in hardware, the overlay is still
  enabled in both shadow and working registers.

- When we unset the manager, the software just configures the overlay's manager
  to point to NULL.

- When we set the overlay to a new manager(which is in auto update) through
  dss_ovl_set_manager, the check  for op->enabled passes, the channel field in
  extra info is set to the new manager. When we do an apply on this manager,
  the new channel out field is set in the hardware immediately, and since the
  overlay enable bit is still set in hardware, the new manager sees that the
  overlay is enabled, and tries to retrieve pixels from it, this leads to sync
  lost as it might be in the middle of processing a frame when we set the
  channel out bit.

The solution to this was to ensure that user space does another update after
disabling the overlay, this actually worked because the overlay was now truly
disabled, and an immediate write to channel out didn't impact since the manager
saw the new overlay as disabled, and doesn't try to retrieve pixels from it.

Remove channel as an extra_info field. Make dss_ovl_unset_manager more strict
about the overlay being disabled when detaching the manager. For overlays
connected to a manual update manager, unset_manager fails if we need another
update to disable the overlay.

We still need to a manual update to ensure the overlay is disabled to get change
the overlay's manager. We could work on doing a dummy update by using DISPC's
capability to gate the different video port signals. This is left for later.

Remove the comment about the sync lost issue.
Signed-off-by: Archit Taneja <archit@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>