libpayload: Add simple hexdump function

- prints hex and ascii
 - detects duplicate all zero lines

Change-Id: I084b3072bc05725b23c5c3ca0dbf1533f164a08c
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: https://gerrit.chromium.org/gerrit/63660
Reviewed-by: David Hendricks <dhendrix@chromium.org>
Commit-Queue: Stefan Reinauer <reinauer@chromium.org>
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Author:  Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: http://review.coreboot.org/4393
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Tested-by: build bot (Jenkins)

payloads/libpayload/include/libpayload.h

@@ -293,6 +293,7 @@ long int labs(long int j);
 long long int llabs(long long int j);
 u8 bin2hex(u8 b);
 u8 hex2bin(u8 h);
+void hexdump(void *memory, int length);
 void fatal(const char *msg) __attribute__ ((noreturn));
 /** @} */