Log unexpected post code from the previous boot

Read out the post code from the previous boot and
log it if the code is not one of the expected values.

Test:
1) interrupt the boot of the system, this is easiest
with warm reset button when servo is attached
2) check the event log with mosys

65 | 2012-09-09 12:32:11 | Last post code in previous boot | 0x9d

Change-Id: Id418f4c0cf005a3e97b8c63de67cb9a09bc57384
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: http://review.coreboot.org/1744
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/include/pc80/mc146818rtc.h

@@ -175,6 +175,10 @@ static inline int get_option(void *dest __attribute__((unused)),
 #define CMOS_POST_BANK_0_OFFSET   (CMOS_POST_OFFSET + 1)
 #define CMOS_POST_BANK_1_MAGIC    0x81
 #define CMOS_POST_BANK_1_OFFSET   (CMOS_POST_OFFSET + 2)
+
+#if !defined(__ROMCC__)
+void cmos_post_log(void);
+#endif
 #endif /* CONFIG_CMOS_POST */
 
 #endif /*  PC80_MC146818RTC_H */