[release,cmake] Corrects the location of Doxyfile in the package configuration.

This completes the last patch where we moved its installation directory by
reflecting the new location in the package configuration.
(cherry picked from commit 69352ecc826aadfe0080a43c6b7680e80efbbfb0)

Signed-off-by: Markus Blatt <markus@dr-blatt.de>