drm/mipi-dsi: Drop MIPI_DSI_MODE_VSYNC_FLUSH flag

Drop the unused MIPI_DSI_MODE_VSYNC_FLUSH flag. Whether or not a display
FIFO flush on vsync is required to avoid sending garbage to the panel is
not a property of the DSI link, but of the integration between display
controller and DSI host bridge.

Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20250627-dsi-vsync-flush-v2-4-4066899a5608@pengutronix.de
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

Author: pH5

include/drm/drm_mipi_dsi.h

@@ -130,8 +130,6 @@ struct mipi_dsi_host *of_find_mipi_dsi_host_by_node(struct device_node *node);
 #define MIPI_DSI_MODE_VIDEO_NO_HBP	BIT(6)
 /* disable hsync-active area */
 #define MIPI_DSI_MODE_VIDEO_NO_HSA	BIT(7)
-/* flush display FIFO on vsync pulse */
-#define MIPI_DSI_MODE_VSYNC_FLUSH	BIT(8)
 /* disable EoT packets in HS mode */
 #define MIPI_DSI_MODE_NO_EOT_PACKET	BIT(9)
 /* device supports non-continuous clock behavior (DSI spec 5.6.1) */