extcon: arizona: Allow configuration of button detection

The Arizona button detection circuit is configurable, allowing the system
integrator to program a range of thresholds for the buttons supported on
the accessory but currently the driver uses the default button ranges and
does not provide any flexibility in how this is exposed to the application
layer.

Provide platform data allowing the user to control this and to map
the buttons to keys in the input subsystem.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>