msm: mdss: Dither support in PingPong buffer

V3 version of mdss dither block has been moved from dspp to
ppb. Based on mdss revision the driver should enable the dither block in
dspp/ppb. Change enables driver to handle dither block in ppb.

Change-Id: Iaa11755b46417db1e2a12cb2f2b6028cd7530c0b
Signed-off-by: Gopikrishnaiah Anandan <agopik@codeaurora.org>
Signed-off-by: Ping Li <pingli@codeaurora.org>