arm: mach-k3: am62: Get soc max temperature by grade

AM62x SoC is available in multiple temperature grade:
- Commercial: 0° to 95° C
- Industrial: -40° to 105° C
- Automotive: -40° to 125° C

Add a new function that returns the am62 max temperature value
accordingly to its temperature grade in Celsius.

Signed-off-by: Joao Paulo Goncalves <joao.goncalves@toradex.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>