bsp: cvitek: fix warning on rtc driver

When RTC is enabled, a warning appear during compiling:
warning: implicit declaration of function 'rtc_alarm_enable' [-Wimplicit-function-declaration]
  366 |     rtc_alarm_enable(alarm->enable);
      |     ^~~~~~~~~~~~~~~~

It's due to _rtc_set_alarm is not covered by RT_USING_ALARM. It's wrong.

Solution: cover all functions including _rtc_get_alarm & _rtc_set_alarm
under RT_USING_ALARM macro conditional defintion.

Signed-off-by: Chen Wang <unicorn_wang@outlook.com>

bsp/cvitek/drivers/drv_rtc.c

@@ -317,7 +317,6 @@ static void rt_hw_rtc_isr(int irqno, void *param)
 
     rt_interrupt_leave();
 }
-#endif
 
 static rt_err_t _rtc_get_alarm(struct rt_rtc_wkalarm *alarm)
 {
@@ -367,6 +366,7 @@ static rt_err_t _rtc_set_alarm(struct rt_rtc_wkalarm *alarm)
 
     return RT_EOK;
 }
+#endif
 
 static const struct rt_rtc_ops _rtc_ops =
 {