ASoC: rt5645: Adds push button support for rt5650

rt5650 support headset button detection. Currently, the button detection
is only implemented for rt5650 codec. The button detection configuration
register's default value is different from rt5645.
And we didn't touch the register in the driver, so we will get the wrong
value when we dump the registers. We will fix it in another patch.

Signed-off-by: Bard Liao <bardliao@realtek.com>
Signed-off-by: Mark Brown <broonie@kernel.org>