msm: mdss: Remove mixer dependency on pingpong Apis

Change the pingpong read and write Apis to accept address,
inorder to support multiple pingpongs accessibility
via same mixer

Change-Id: Ia21ee21fbb8d4334d6cdc8b7b659f6f263222a69
Signed-off-by: Kalyan Thota <kalyant@codeaurora.org>