[MINI FEATURE] get (first) coretemp temperature

[daringer]

There is a request to provide a max temperature from CPU and GFX temperature from issue #47 .

"The internet" states this, but looks like here is even a walkthrough how to hack this into the kernel. Here there might be some ideas on how to directly access the appropriate hwmon device without the file system detour ....

This should be quite straight forward:

• extend hwmon_attr by one
• create new hwmon attribute temp_merged_max like here
• register it here
• write getter function using the hints above