cpufreq: Move org.gnome.CPUFreqSelector.conf to /usr/share/dbus-1/system.d

This fixes the following warning from Debian's Lintian tool:

The package contains D-Bus policy configuration and installs it under /etc/dbus-1/system.d or /etc/dbus-1/session.d. These directories are reserved for local configuration, which overrides the default policies in /usr.

The correct directory for system bus policy installed by packages is /usr/share/dbus-1/system.d.

The correct directory for session bus policy installed by packages (not usually needed) is /usr/share/dbus-1/session.d.

Please refer to the dbus-daemon(1) manual page for details.