fastboot: Make tags_offset a command line option.

This matches what mkbootimg supports in 5d4af6314fded027952941110a520dc9aa234a14

It will allow "fastboot flash:raw ..." to work for devices that need tags_offset.

Change-Id: I4ceca528f88cc8ede5742f8a67bec972e41eebe7
diff --git a/fastboot/fastboot.c b/fastboot/fastboot.c
index 73a6e56..7d26c6f 100644
--- a/fastboot/fastboot.c
+++ b/fastboot/fastboot.c
@@ -889,6 +889,7 @@
         {"kernel_offset", required_argument, 0, 'k'},
         {"page_size", required_argument, 0, 'n'},
         {"ramdisk_offset", required_argument, 0, 'r'},
+        {"tags_offset", required_argument, 0, 't'},
         {"help", 0, 0, 'h'},
         {0, 0, 0, 0}
     };
@@ -897,7 +898,7 @@
 
     while (1) {
         int option_index = 0;
-        c = getopt_long(argc, argv, "wub:k:n:r:s:S:lp:c:i:m:h", longopts, NULL);
+        c = getopt_long(argc, argv, "wub:k:n:r:t:s:S:lp:c:i:m:h", longopts, NULL);
         if (c < 0) {
             break;
         }
@@ -938,6 +939,9 @@
         case 'r':
             ramdisk_offset = strtoul(optarg, 0, 16);
             break;
+        case 't':
+            tags_offset = strtoul(optarg, 0, 16);
+            break;
         case 's':
             serial = optarg;
             break;