msm: mdss: free framebuffer pipes on suspend

When going to suspend, need to clear the frame buffer pipes allocated
since these were allocated by driver. These will get reallocated
automatically on resume.

Change-Id: I3c5697277edfc8f976a0720f5f94f10314f5ebe6
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>