iio: temperature: ltc2983: Add support for ADT7604

iio: temperature: ltc2983: Add support for ADT7604

The ADT7604 shares the same die as the LTC2984. It repurposes the
custom RTD sensor type (18) as a copper trace resistance sensor
and the custom thermistor type (27) as a leak detector, and
removes thermocouple, diode and direct ADC sensor types.

Two new software sensor type values are introduced
(LTC2983_SENSOR_COPPER_TRACE = 32, LTC2983_SENSOR_LEAK_DETECTOR = 33)
that map to the hardware register values 18 and 27 respectively.
Dedicated structs (ltc2983_copper_trace, ltc2983_leak_detector) and
parser functions are added rather than extending the existing RTD and
thermistor paths, as the hardware configuration bits are fully
hardcoded and several RTD/thermistor properties would need to be
explicitly forbidden or ignored.

Custom RTD (type 18) becomes the copper trace sensor. Sensor
configuration bits are hardcoded to 0b1001 per the datasheet.
Two variants are supported via the adi,copper-trace-sub-ohm DT
property: sub-ohm traces (< 1 ohm) have bits 17:0 cleared with no
excitation current or custom table; standard traces (> 1 ohm) have
a required resistance-to-temperature table.

Custom thermistor (type 27) becomes the leak detector. Sensor
configuration bits are hardcoded to 0b001. The custom table uses
a resolution of 16 instead of 64, and is specified via the
required adi,custom-leak-detector DT property.

Both sensor types expose an IIO_RESISTANCE channel reading from
the resistance result register bank (0x0060-0x00AF). Added a
"base" parameter to the LTC2983_RESULT_ADDR macro and a "base_reg"
parameter to the ltc2983_chan_read function so we can read from
both result register banks. The resistance register encodes the
measured resistance with 10 fractional bits, so dividing by 1024
gives ohms. Since the sense resistor is specified in ohms, the
output is in ohms for both sensor types and a single 1/1024
scale applies to both. For > 1 ohm copper traces and for leak
detectors, a secondary channel also appears: IIO_TEMP
(millidegrees Celsius) for copper trace and IIO_COVERAGE (percent)
for leak detector.

The ltc2983_chip_info struct is extended with a u64 supported_sensors
bitmask using BIT_ULL() to safely represent the new sensor type bits
32 and 33 on 32-bit builds. A LTC2983_SENSOR_NUM sentinel is added
to the enum so that the bounds check uses >= LTC2983_SENSOR_NUM
rather than hardcoding the last sensor type.

Tested on EVAL-ADT7604-AZ connected to Raspberry Pi 5 via SPI.

Signed-off-by: Liviu Stan <liviu.stan@analog.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>