ASoC: rt5663: Add the manual offset field to compensate the DC offset

The patch adds the manual offset field in the devicetree to compensate the
DC offset that will be different between the PCB layout. It only can be
measured by the real production.

Signed-off-by: Oder Chiou <oder_chiou@realtek.com>
Signed-off-by: Mark Brown <broonie@kernel.org>