drm/bridge: ti-sn65dsi86: Fix 0-day build error

0day reports:

>> drivers/gpu/drm/bridge/ti-sn65dsi86.o: In function
mipi_dsi_detach'
>> drivers/gpu/drm/bridge/ti-sn65dsi86.c:630: undefined reference to
ti_sn_bridge_attach':
>> drivers/gpu/drm/bridge/ti-sn65dsi86.c:249: undefined reference to
mipi_dsi_device_register_full'
>> drivers/gpu/drm/bridge/ti-sn65dsi86.c:276: undefined reference to
mipi_dsi_device_unregister'

Quite obviously the driver depends on DRM_MIPI_DSI.
We can not use depends since the driver configuration uses select,
so we'll have to select the missing dependency instead.

Cc: Sean Paul <seanpaul@chromium.org>
Cc: Dylan Reid <dgreid@chromium.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180815194923.3258-1-sean@poorly.run

drivers/gpu/drm/bridge/Kconfig

@@ -142,6 +142,7 @@ config DRM_TI_SN65DSI86
 	select DRM_KMS_HELPER
 	select REGMAP_I2C
 	select DRM_PANEL
+	select DRM_MIPI_DSI
 	help
 	  Texas Instruments SN65DSI86 DSI to eDP Bridge driver