iio: srf04: add support for power management

This patchset adds support for power management for the srf04 iio driver. It was suggested by Franz for the purpose of saving energy on battery driven vehicles.

Changes in v3:
Thanks to Jonathan for reviewing:
- drop CONFIG_PM
- use __maybe_unused for suspend and resume functions

Changes in v2:
Thanks to Rob for pointing out some improvements in dt-binding:
- add minimum, maximum and default value for startup-time-ms
- drop schema reference

Andreas Klinger (2):
dt-bindings: devantech-srf04.yaml: add pm feature
iio: srf04: add power management feature

 .../iio/proximity/devantech-srf04.yaml        | 18 ++++
 drivers/iio/proximity/srf04.c                 | 96 ++++++++++++++++++-
 2 files changed, 113 insertions(+), 1 deletion(-)

2.20.1