LWMON5: POST RTC fix

Modify the RTC API to provide one a status for the time reported by
the rtc_get() function:
  0 - a reliable time is guaranteed,
< 0 - a reliable time isn't guaranteed (power fault, clock issues,
      and so on).

The RTC chip drivers are responsible for providing this info if the
corresponding chip supports such functionality. If not - always
report that the time is reliable.

The POST RTC test was modified to detect the RTC faults utilizing
this new rtc_get() feature.

Signed-off-by: Yuri Tikhonov <yur@emcraft.com>
diff --git a/drivers/rtc/mcfrtc.c b/drivers/rtc/mcfrtc.c
index 27386e5..d235d10 100644
--- a/drivers/rtc/mcfrtc.c
+++ b/drivers/rtc/mcfrtc.c
@@ -39,7 +39,7 @@
 #define isleap(y) ((((y) % 4) == 0 && ((y) % 100) != 0) || ((y) % 400) == 0)
 #define	STARTOFTIME		1970
 
-void rtc_get(struct rtc_time *tmp)
+int rtc_get(struct rtc_time *tmp)
 {
 	volatile rtc_t *rtc = (rtc_t *) (CFG_MCFRTC_BASE);
 
@@ -64,6 +64,8 @@
 	       tmp->tm_year, tmp->tm_mon, tmp->tm_mday, tmp->tm_wday,
 	       tmp->tm_hour, tmp->tm_min, tmp->tm_sec);
 #endif
+
+	return 0;
 }
 
 void rtc_set(struct rtc_time *tmp)