cbfstool: Add bintohex function

We need to emit some hex strings.

Change-Id: I9e7e184282f6ad0470f2e269f5dc874e78f8b697
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/11766
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

util/cbfstool/common.h

@@ -210,4 +210,11 @@ extern struct xdr xdr_le, xdr_be;
 size_t bgets(struct buffer *input, void *output, size_t len);
 size_t bputs(struct buffer *b, const void *data, size_t len);
 
+/* Returns a 0-terminated string containing a hex representation of
+ * len bytes starting at data.
+ * The string is malloc'd and it's the caller's responsibility to free
+ * the memory.
+ * On error, bintohex returns NULL.
+ */
+char *bintohex(uint8_t *data, size_t len);
 #endif