params: add cpu_custom_temp_sensor

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This is useful for arm boards which might have different sensor names because of different kernel device trees.

This parameter accepts two arguments separated by comma:

1. hwmon sensor name
2. hwmon sensor file

example: cpu_custom_temp_sensor=coretemp,temp7_input

Will try to use hwmon sensor whose '/sys/class/hwmon/hwmon[0-9]+/name' file contents equals 'coretemp' and, and try to use 'temp7_input' file