sound_control: initial code push for Headphones gain userspace interface.

Signed-off-by: Francisco Franco <franciscofranco.1990@gmail.com>
sound_control: add headset, speaker and mic gain interfaces. Also add the sysfs control file.

Signed-off-by: Francisco Franco <franciscofranco.1990@gmail.com>
sound_control: add workaround to prevent audio resets after using custom values. Based on https://github.com/faux123/Nexus_5/commit/33407fd2d63290540eb0054bc7c6611f2080ea8b

Signed-off-by: Francisco Franco <franciscofranco.1990@gmail.com>