mkimage: Allow updating the FIT timestamp

Normally the FIT timestamp is created the first time mkimage is run on a
FIT, when converting the source .its to the binary .fit file. This
corresponds to using the -f flag. But if the original input to mkimage is
a binary file (already compiled) then the timestamp is assumed to have
been set previously.

Add a -t flag to allow setting the timestamp in this case.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/tools/mkimage.c b/tools/mkimage.c
index 7cb666d..43078d0 100644
--- a/tools/mkimage.c
+++ b/tools/mkimage.c
@@ -145,7 +145,7 @@
 	int opt;
 
 	while ((opt = getopt(argc, argv,
-			     "a:A:b:B:c:C:d:D:e:Ef:Fk:i:K:ln:N:p:O:rR:qsT:vVx")) != -1) {
+		   "a:A:b:B:c:C:d:D:e:Ef:Fk:i:K:ln:N:p:O:rR:qstT:vVx")) != -1) {
 		switch (opt) {
 		case 'a':
 			params.addr = strtoull(optarg, &ptr, 16);
@@ -269,6 +269,9 @@
 		case 's':
 			params.skipcpy = 1;
 			break;
+		case 't':
+			params.reset_timestamp = 1;
+			break;
 		case 'T':
 			if (strcmp(optarg, "list") == 0) {
 				show_valid_options(IH_TYPE);