msm: VPU: Add 4th pipe for display output port

The current code only provides an interface for 3 display pipes, when four
pipes can actually be set. This changes provides the interface to set the
fourth display pipe.

Change-Id: I214e73bd1bd8940b4b2744b9b654b7563004f1f3
Signed-off-by: Stephane Viau <sviau@codeaurora.org>