iio: proximity: IQS2x3 v14 IRQ edge

iio: proximity: IQS2x3 v14 IRQ edge

- Add a DT option to select interrupt trigger type.
- Change gpio_get_value calls to gpio_get_value_cansleep in case a GPIO
  expander is used.
- Update documentation for the DT option.

Bug 200129230

Change-Id: Iebdb89dabddf05a09c2c9d36cc3cf3592806b58e
Signed-off-by: Erik Lilliebjerg <elilliebjerg@nvidia.com>
Reviewed-on: http://git-master/r/787380
(cherry picked from commit efe0df79fc1f4313fa49673b5c6dedc3d5fb4fef)
Reviewed-on: http://git-master/r/792010
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Robert Collins <rcollins@nvidia.com>
Tested-by: Robert Collins <rcollins@nvidia.com>