udev-seat: Make the udev_input structure an embedded structure

And as a result of this stop iterating through the compositor seat list
(of one item) and instead access the udev_input structure directly.

This enables a refactoring to pull out the weston_seat into a separate
structure permitting multiple seats.
diff --git a/src/compositor-fbdev.c b/src/compositor-fbdev.c
index 43897da..605dcd8 100644
--- a/src/compositor-fbdev.c
+++ b/src/compositor-fbdev.c
@@ -52,6 +52,7 @@
 
 	struct udev *udev;
 	struct tty *tty;
+	struct udev_input input;
 };
 
 struct fbdev_screeninfo {
@@ -751,11 +752,8 @@
 fbdev_compositor_destroy(struct weston_compositor *base)
 {
 	struct fbdev_compositor *compositor = to_fbdev_compositor(base);
-	struct udev_input *input, *next;
 
-	/* Destroy all inputs. */
-	wl_list_for_each_safe(input, next, &compositor->base.seat_list, base.link)
-		udev_input_destroy(input);
+	udev_input_destroy(&compositor->input);
 
 	/* Destroy the output. */
 	weston_compositor_shutdown(&compositor->base);
@@ -771,7 +769,6 @@
 vt_func(struct weston_compositor *base, int event)
 {
 	struct fbdev_compositor *compositor = to_fbdev_compositor(base);
-	struct udev_input *input;
 	struct weston_output *output;
 
 	switch (event) {
@@ -786,13 +783,11 @@
 
 		weston_compositor_damage_all(&compositor->base);
 
-		wl_list_for_each(input, &compositor->base.seat_list, base.link)
-			udev_input_enable(input, compositor->udev);
+		udev_input_enable(&compositor->input, compositor->udev);
 		break;
 	case TTY_LEAVE_VT:
 		weston_log("leaving VT\n");
-		wl_list_for_each(input, &compositor->base.seat_list, base.link)
-			udev_input_disable(input);
+		udev_input_disable(&compositor->input);
 
 		wl_list_for_each(output, &compositor->base.output_list, link) {
 			fbdev_output_disable(output);
@@ -884,7 +879,7 @@
 	if (fbdev_output_create(compositor, param->device) < 0)
 		goto out_pixman;
 
-	udev_input_create(&compositor->base, compositor->udev, seat);
+	udev_input_init(&compositor->input, &compositor->base, compositor->udev, seat);
 
 	return &compositor->base;