Many of the Rockchip SoCs support storing trim values for the sensors in
factory programmable memory. These values specify a fixed offset from
the sensor's returned temperature to get a more accurate picture of what
temperature the silicon is actually at.

The way this is implemented is with various OTP cells, which may be
absent. There may both be whole-TSADC trim values, as well as per-sensor
trim values.

In the downstream driver, whole-chip trim values override the per-sensor
trim values. This rewrite of the functionality changes the semantics to
something I see as slightly more useful: allow the whole-chip trim
values to serve as a fallback for lacking per-sensor trim values,
instead of overriding already present sensor trim values.

Additionally, the chip may specify an offset (trim_base, trim_base_frac)
in degrees celsius and degrees decicelsius respectively which defines
what the basis is from which the trim, if any, should be calculated
from. By default, this is 30 degrees Celsius, but the chip can once
again specify a different value through OTP cells.

The implementation of these trim calculations have been tested
extensively on an RK3576, where it was confirmed to get rid of pesky 1.8
degree Celsius offsets between certain sensors.

Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>