lib: time: export usec_to_tick()

In the UEFI Stall() boottime service we need access to usec_to_tick().

Export the function.

Remove redundant implementation in arch/arm/mach-rockchip/rk_timer.c.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

arch/arm/mach-rockchip/rk_timer.c

@@ -20,13 +20,6 @@ static uint64_t rockchip_get_ticks(void)
 	return timebase_h << 32 | timebase_l;
 }
 
-static uint64_t usec_to_tick(unsigned int usec)
-{
-	uint64_t tick = usec;
-	tick *= CONFIG_SYS_TIMER_RATE / (1000 * 1000);
-	return tick;
-}
-
 void rockchip_udelay(unsigned int usec)
 {
 	uint64_t tmp;