ASoC: rt5645: improve headphone depop function

We add a calibration function and call it at the beginning of i2c_probe.
The calibration value will be kept until codec is shutdown. We will reset
the codec after the calibration is finished. So, we set cache_bypass in
the calibration function. The benefit is we can shorter the delay time
in headphone depop.

We also change the register setting in the depop sequence which will
reduce the pop noise in headphone playback.
Signed-off-by: John Lin <john.lin@realtek.com>
Signed-off-by: Mark Brown <broonie@kernel.org>