Enable fastboot feature on rk3288.
This path doesn't support the fastboot flash function command entirely.
We will hit "cannot find partition" assertion without specified
partition environment. Define gpt partition layout in specified board
such as firefly-rk3288, then enjoy it!
Signed-off-by: Ziyuan Xu <xzy.xu@rock-chips.com>
Acked-by: Simon Glass <sjg@chromium.org>