Add Support for GPU Clock Frequencies (sclk and mclk) in hwmon Collector

[zxhdaze]

Hi, I would like to propose an enhancement to the hwmon collector to include GPU clock. Currently on my machine I can pull the GPU clock metrics from hwmon:

/sys/class/hwmon/hwmon0/freq1_input:214000000
/sys/class/hwmon/hwmon0/freq1_label:sclk
/sys/class/hwmon/hwmon0/freq2_input:300000000
/sys/class/hwmon/hwmon0/freq2_label:mclk

However, they are not collected by the collector. I propose to add the clock frequencies support.