Conditionally #include mc1468181rtc if CMOS_POST is enabled

This will omit the mc1468181rtc header if it is not needed. Currently
it contains a lot of inlined functions which depend on architecture-
specific IO.

Change-Id: I4ef1bc1362c159e0c780c3eade01af04f029f949
Signed-off-by: David Hendricks <dhendrix@chromium.org>
Reviewed-on: http://review.coreboot.org/1916
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
Tested-by: build bot (Jenkins)

src/console/post.c

@@ -21,7 +21,9 @@
 
 #include <arch/io.h>
 #include <console/console.h>
+#if CONFIG_CMOS_POST
 #include <pc80/mc146818rtc.h>
+#endif
 #include <elog.h>
 
 /* Write POST information */