Fix dependencies

As a user on the tuned-git AUR page made me aware, as for some reason it only ever was discussed there, apparently some dependencies need to be changed. Hence I've gone through the code and checked every reference:

• tuned apparently needs the kernel perf package that is perf and not python-perf
• dbus-glib is not needed as only ever the glib bindings from python-dbus are used
• x86_energy_perf_policy is an optional depedency used for a plugin to set the performance and energy bias hint for the kernel

Additionally I just changed the capitalization of the optional dependencies as it is done this way for other packages.

Cheers.

Fixes #1 (closed).