lib: time: add weak timer_init() function

If timer_init() is made a weak stub function, then it allows us to
remove several empty timer_init functions for those boards that
already have a timer initialized when u-boot starts. Architectures
that use the timer framework may also remove the need for timer.c.

Signed-off-by: Darwin Rambo <drambo@broadcom.com>
Reviewed-by: Tim Kryger <tim.kryger@linaro.org>

lib/time.c

@@ -60,6 +60,11 @@ static unsigned long long notrace tick_to_time(uint64_t tick)
 	return tick;
 }
 
+int __weak timer_init(void)
+{
+	return 0;
+}
+
 ulong __weak get_timer(ulong base)
 {
 	return tick_to_time(get_ticks()) - base;