fastboot: support for overriding format fs-type and size

This changes allows overriding the fs-type and size that
are normally returned by the booloader.

This is in preparation for supporting other FSes.

Change-Id: I8d141a0d4d14df9fe84d3b131484e9696fcd8870
Signed-off-by: JP Abgrall <jpa@google.com>
diff --git a/fastboot/engine.c b/fastboot/engine.c
index 0fab703..5a6709b 100644
--- a/fastboot/engine.c
+++ b/fastboot/engine.c
@@ -102,18 +102,20 @@
  * Not all devices report the filesystem type, so don't report any errors,
  * just return false.
  */
-int fb_format_supported(usb_handle *usb, const char *partition)
+int fb_format_supported(usb_handle *usb, const char *partition, const char *type_override)
 {
-    char response[FB_RESPONSE_SZ + 1] = {0,};
+    char fs_type[FB_RESPONSE_SZ + 1] = {0,};
     int status;
     unsigned int i;
 
-    status = fb_getvar(usb, response, "partition-type:%s", partition);
+    if (type_override) {
+        return !!fs_get_generator(type_override);
+    }
+    status = fb_getvar(usb, fs_type, "partition-type:%s", partition);
     if (status) {
         return 0;
     }
-
-    return !!fs_get_generator(response);
+    return !!fs_get_generator(fs_type);
 }
 
 static int cb_default(Action *a, int status, char *resp)