meta-ampere: handle Overtemp Fault LED

Assert Fault LED when detecting OVERTEMP signal asserted.
This is done by adding new overtemp_fault LED group and
update the overtemp service to assert/de-assert the LED
group.

1. Start the ampere_overtemp@.service
2. Verify that the `Fault Led` is turned on and turn off after 10s.
3. Verify that Thermal Trip SEL is created.

Signed-off-by: Hieu Huynh <hieuh@os.amperecomputing.com>
Change-Id: Ifbc203bf79a13741082d84850b9e75ca6148a6cd