thermal: tegra: get rid of PDIV/HOTSPOT hack

Get rid of T124-specific PDIV/HOTSPOT hack.
tegra-soctherm.c contained a hack to set the SENSOR_PDIV and
SENSOR_HOTSPOT_OFFSET registers - it just did two writes of
T124-specific opaque values.  Convert these into a form that can be
substituted on a per-chip basis, and into structure fields that have
at least some independent meaning.

Signed-off-by: Wei Ni <wni@nvidia.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>