MBHC (MultiButton Headset Control) support is available in pm8921 in two
blocks, one to detect mechanical headset insertion and removal and other
block to support headset type detection and 5 button detection and othe
features like impedance calculation.

This patch adds support to:
1> Support to NC and NO type of headset Jacks.
2> Mechanical insertion and detection of headset jack.
3> Detect a 3 pole Headphone and a 4 pole Headset.
4> Detect 5 buttons.

Tested it on DB410c with Audio Mezz board with 4 pole and 3 pole
headset/headphones.
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Tested-by: Damien Riegel <damien.riegel@savoirfairelinux.com>
Signed-off-by: Mark Brown <broonie@kernel.org>