Merge pull request ARMmbed#12081 from micgur01/master

Expose target_offset and header_offset parameters in targets.json

Author: 0xc0170

targets/targets.json

@@ -38,6 +38,14 @@
                 "help": "Time in ms required to go to and wake up from deep sleep (max 10)",
                 "value": 0
             },
+            "app_offset": {
+                "help": "Application start offset in ROM",
+                "value": null
+            },
+            "header_offset": {
+                "help": "Application header offset in ROM",
+                "value": null
+            },
             "boot-stack-size": {
                 "help": "Define the boot stack size in bytes. This value must be a multiple of 8",
                 "value": "0x1000"