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_plmt.c

@@ -43,7 +43,7 @@ static const struct fdt_match timer_plmt_match[] = {
 	{},
 };
 
-struct fdt_timer fdt_timer_plmt = {
+const struct fdt_driver fdt_timer_plmt = {
 	.match_table = timer_plmt_match,
-	.cold_init   = fdt_plmt_cold_timer_init,
+	.init = fdt_plmt_cold_timer_init,
 };