The old mode uses soft timer to update received data,
which costs much cpu resource, even though there is no
data. The new mode is based on uart time out, it updates
data only when transfer completes.
Change-Id: Id12e351ff00015e4bfb36f416731ce4af5330001
Signed-off-by: Huibin Hong <huibin.hong@rock-chips.com>