msm: mdss: Fix incorrect pp flush programming for apq8084

In apq8084 flush bits for newly added layer mixer 5 and DSPP 3 are not
symmetrically aligned with other layer mixers and DSPPs. Current post
processing code does not consider this and configures wrong flush bits.
Fix this by updating correct flush bits.

Change-Id: I150f58405f343239d167c4ad6feb991aa7cb61d2
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>