msm: mdss: Add support for additional pipes of apq8084 MDSS

APQ8084 MDSS has 2 extra pipes compare to MDSS of msm8974. This change
adds support for programming these new pipes and corresponding mixer and
control pipeline changes.

Change-Id: I1406263de703719661789d2f8c6f7c06fc810919
Signed-off-by: Shalabh Jain <shalabhj@codeaurora.org>
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>