Export install location for DBUS interfaces via CMake

Authored by bruns on Sep 3 2018, 1:15 AM.

Description

Export install location for DBUS interfaces via CMake

Summary:
This is useful for any other package depending on the interface
description at build time, and mimics other packages which export
DBUS interfaces.

Reviewers: Plasma, davidedmundson

Reviewed By: Plasma, davidedmundson

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D15228