msm: mdss: Make DSPP PP setup more modular

The previous DSPP PP setup function included config functions for each
of the different PP blocks except for dither. Now there is a dither setup
function, as well as an opmode setup function in order to clean up what is
done inside DSPP PP setup.

Change-Id: Ia347c35bb675e20531272566647a364f6e68468c
Signed-off-by: Benet Clark <benetc@codeaurora.org>