Add simple hexdump function

- prints hex and ascii
 - detects duplicate all zero lines

BUG=none
TEST=none
BRANCH=none

Change-Id: I557fed34f0f50ae256a019cf893004a0d6cbff7c
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: https://gerrit.chromium.org/gerrit/62655
Reviewed-by: David Hendricks <dhendrix@chromium.org>
Tested-by: Stefan Reinauer <reinauer@chromium.org>
Commit-Queue: Stefan Reinauer <reinauer@chromium.org>

src/include/lib.h

@@ -54,4 +54,7 @@ void cache_as_ram_main(void);
 void cache_as_ram_main(unsigned long bist, unsigned long cpu_init_detectedx);
 #endif
 
+/* Defined in src/lib/hexdump.c */
+void hexdump(unsigned long memory, int length);
+
 #endif /* __LIB_H__ */