sensors: Add separation between ambient and die temperature

Some device include a temperature sensor, usually used as a
companion for helping in drift compensation, that measure the
die temperature. This temperature IS NOT related to the the
ambient temperature, hence a clean separation between the two
is required.

This commit introduces a clean separation between the two
types of temperature leaving the old deprecated definition
still there.

The list of current drivers that read the die (and not the ambient)
temperature is the following:

 - adxl362
 - bma280
 - bmg160
 - bmi160
 - fxos8700
 - lis3mdl
 - lsm6ds0
 - lsm6dsl
 - lsm9ds0
 - mpu6050

Signed-off-by: Armando Visconti <armando.visconti@st.com>