Support intel-pstate driver.

Intel P-state driver was introduced in linux-3.9 (default in linux-3.10 I
think)and doesn't support directly frequencies. It allows only to switch
between the two available governors: performance and powersave. Show the
governor name instead of the frequency
Capitalize the first letter of the governor names.

Just nicer IMHO.
Add basic Makefile to install the extension in the local home dir.

The polkit policy is not installed.