timer: Allow delays with a 32-bit microsecond timer

The current get_timer_us() uses 64-bit arithmetic on 32-bit machines.
When implementing microsecond-level timeouts, 32-bits is plenty. Add a
new function that uses an unsigned long. On 64-bit machines this is
still 64-bit, but this doesn't introduce a penalty. On 32-bit machines
it is more efficient.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

lib/time.c

@@ -152,6 +152,11 @@ uint64_t __weak get_timer_us(uint64_t base)
 	return tick_to_time_us(get_ticks()) - base;
 }
 
+unsigned long __weak get_timer_us_long(unsigned long base)
+{
+	return timer_get_us() - base;
+}
+
 unsigned long __weak notrace timer_get_us(void)
 {
 	return tick_to_time(get_ticks() * 1000);