drm/panel/panel-sitronix-st7701: Make DSI mode flags common to ST7701

The ST7701 and ST7701S are TFT matrix drivers with integrated multi
protocol decoder capable of DSI/DPI/SPI input and 480x360...864 line
TFT matrix output. Currently the only supported input is DSI.

The protocol decoder is separate from the TFT matrix driver and is
always capable of handling all of DSI non-burst mode with sync pulses
or sync events as well as DSI burst mode.

Move the DSI mode configuration from TFT matrix driver properties to
common ST7701 code, because this is common to all TFT matrices.

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>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220710194437.289042-1-marex@denx.de