drm/panel: sitronix-st7789v: add support for partial mode

The ST7789V controller features support for the partial mode. Here,
the area to be displayed can be restricted in one direction (by default,
in vertical direction). This is useful for panels that are partially
occluded by design. Add support for the partial mode.

Signed-off-by: Michael Riesch <michael.riesch@wolfvision.net>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230718-feature-lcd-panel-v2-3-2485ca07b49d@wolfvision.net