drm/panel/panel-sitronix-st7701: Enable DSI burst mode, LPM, non-continuous clock

drm/panel/panel-sitronix-st7701: Enable DSI burst mode, LPM, non-continuous clock

The ST7701(S) is capable of DSI burst mode, which is more energy
efficient than the non-burst modes. Make use of it.

The ST7701(S) is capable of DSI non-continuous clock, since it
sources the TFT matrix driver clock from internal clock source.
The DSI non-continuous clock further reduce power utilization.

The ST7701(S) uses DSI LPM for command transmissions, make sure
this is configured correctly in the DSI mode flags.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Guido Günther <agx@sigxcpu.org>
Cc: Jagan Teki <jagan@amarulasolutions.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220710194437.289042-2-marex@denx.de