mx8m:bootscript-uboot: Apply temperature grade overlays

The bootscript checks now if the cpu_temp_grade var is set in the u-boot
environment. If so, the scripts tries to load the corresponding overlay.
According to the u-boot cpu_get_temp_grade function, the critical extended
commercial temp is equal to the industrial temp. Therefore, the industrial
overlay is also applied for the extended commercial grade.
Deploy industrial temp overlay for mx8mp and mx8mm. The automotive overlay
is not deployed, since mx8mp and mx8mm SoCs are only available in consumer
and industrial versions at the moment.
The default values in devicetree match the consumer/commercial grade.

BCS 746-001385