drm/uapi: Add USB connector type

Add a connector type for USB connected display panels.

Some examples of what current userspace will name the connector:
- Weston: "UNNAMED-%d"
- Mutter: "Unknown20-%d"
- X: "Unknown20-%d"

v2:
- Update drm_connector_enum_list
- Add examples to commit message
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210313112545.37527-2-noralf@tronnes.org

drivers/gpu/drm/drm_connector.c

@@ -94,6 +94,7 @@ static struct drm_conn_prop_enum_list drm_connector_enum_list[] = {
 	{ DRM_MODE_CONNECTOR_DPI, "DPI" },
 	{ DRM_MODE_CONNECTOR_WRITEBACK, "Writeback" },
 	{ DRM_MODE_CONNECTOR_SPI, "SPI" },
+	{ DRM_MODE_CONNECTOR_USB, "USB" },
 };
 
 void drm_connector_ida_init(void)

include/uapi/drm/drm_mode.h

@@ -388,6 +388,7 @@ enum drm_mode_subconnector {
 #define DRM_MODE_CONNECTOR_DPI		17
 #define DRM_MODE_CONNECTOR_WRITEBACK	18
 #define DRM_MODE_CONNECTOR_SPI		19
+#define DRM_MODE_CONNECTOR_USB		20
 
 /**
  * struct drm_mode_get_connector - Get connector metadata.