msm: mdss: reset control path configuration during panel off

Because of the dynamic way that control paths can be configured, a
different control path can be used for different panel interfaces.
In order to avoid same panel and/or same mixer being configured for same
control path, ensure the control path configuration is completely
cleared once it's no longer active.

Change-Id: I090cfd0b325100363de3d3fcc49c364b93619093
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>