RFC iio: proximity: Add Cytron HC-SR04 support

Add Device Tree binding and driver match support for the Cytron HC-SR04 ultrasonic distance sensor.

The HC-SR04 uses separate trigger and echo GPIOs. A trigger pulse of at least 10 us starts a measurement, and the echo pulse width reports the ultrasonic round-trip time. This matches the protocol already implemented by the SRF04 IIO driver.

The series adds the Cytron vendor prefix, documents the cytron,hc-sr04 compatible, and uses the existing SRF04 configuration in the driver.

The Cytron vendor attribution is based on the HC-SR04 Product User's Manual V1.0 supplied by the retailer. The manual was prepared by Cytron Technologies Sdn. Bhd. and contains Cytron warranty and support information.

This is sent as an RFC because the vendor attribution and compatible name should be reviewed.

Testing:
- make dt_binding_check: PASS
- srf04 module build: PASS
- Tested on Raspberry Pi 3 Model B+
- Kernel: 6.18.34+rpt-rpi-v8
- Device instantiated using only cytron,hc-sr04
- Trigger connected to GPIO17
- Echo connected to GPIO27 through a 5 V to 3.3 V resistor divider
- Driver bound and registered an IIO device
- in_distance_raw returned changing distance readings

Paweł Wiśniewski (3):
dt-bindings: vendor-prefixes: Add Cytron Technologies
dt-bindings: iio: proximity: Add Cytron HC-SR04
iio: proximity: srf04: Add Cytron HC-SR04 support

 .../devicetree/bindings/iio/proximity/devantech-srf04.yaml   | 5 ++++-
 Documentation/devicetree/bindings/vendor-prefixes.yaml       | 2 ++
 drivers/iio/proximity/Kconfig                                | 1 +
 drivers/iio/proximity/srf04.c                                | 1 +
 4 files changed, 8 insertions(+), 1 deletion(-)

base-commit: 37e2f878a7a660a216cc7a60459995fefd150f25

2.47.3