Merge UDP fastboot support from AOSP:

  https://android.googlesource.com/platform/external/u-boot/+/android-o-mr1-iot-preview-8

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
Signed-off-by: Alex Deymo <deymo@google.com>
Signed-off-by: Jocelyn Bohr <bohr@google.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

Rename fb_set_reboot_flag to fastboot_set_reboot_flag so it matches
all other fastboot code in the global name space. Fix the guards around
them so that they're dependent on FASTBOOT, not just USB_FUNCTION_FASTBOOT.

Move the weak implementation of fastboot_set_reboot_flag to fb_common.c
so we can call it from non-USB fastboot code.

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>

Add drivers/fastboot/fb_common.c, where fastboot_okay/fail are implemented
so we can call them from a non-USB implementation.

Introduce fastboot_response which takes varargs parameters so we can
use it to generate formatted response strings. Refactor fastboot_okay/fail
to use it.

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>