Merge UDP fastboot support from AOSP:

  https://android.googlesource.com/platform/external/u-boot/+/android-o-mr1-iot-preview-8Signed-off-by: NAlex Kiernan <alex.kiernan@gmail.com>
Signed-off-by: NAlex Deymo <deymo@google.com>
Signed-off-by: NJocelyn Bohr <bohr@google.com>
Reviewed-by: NSimon Glass <sjg@chromium.org>