lib: utils/timer: Use fdt_driver for initialization

The timer driver subsystem does not need any extra data, so it can use
`struct fdt_driver` directly. The generic fdt_timer_init() performs a
best-effort initialization of all matching DT nodes.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org>

lib/utils/timer/fdt_timer_mtimer.c

@@ -162,7 +162,7 @@ static const struct fdt_match timer_mtimer_match[] = {
 	{ },
 };
 
-struct fdt_timer fdt_timer_mtimer = {
+const struct fdt_driver fdt_timer_mtimer = {
 	.match_table = timer_mtimer_match,
-	.cold_init = timer_mtimer_cold_init,
+	.init = timer_mtimer_cold_init,
 };