drm/mcde: Fix frame sync setup for video mode panels

drm/mcde: Fix frame sync setup for video mode panels

The MCDE driver differentiates only between "te_sync"
(for hardware TE0 sync) and software sync
(i.e. manually triggered updates) at the moment.

However, none of these options work correctly for video mode panels.
Therefore, we need to make some changes to make them work correctly:

  - Select hardware sync coming from the (DSI) formatter.
  - Keep the FIFO permanently enabled (otherwise MCDE will stop
    feeding data to the panel).
  - Skip manual software sync (this is not necessary in video mode).

Automatically detect if the connected panel is using video mode
and enable the necessary changes in that case.

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191106165835.2863-3-stephan@gerhold.net