msm:cpp: Enable two paralel to planar output in cpp

Add second pointer that is used when conversion from
two planar to three planar format  is needed. The
two pointers will help to write the two output chroma
planes in paralel.

Change-Id: Iab1f885c0289f76805f7241549590803f0d15060
Signed-off-by: Iliya Varadzhakov <ivarad@codeaurora.org>