drm/msm/mdp5: Start using parameters from CRTC state

In the last few commits, we've been adding params to mdp5_crtc_state, and
assigning them in the atomic_check() funcs. Now it's time to actually
start using them.

Remove the duplicated params from the mdp5_crtc struct, and start using
them in the mdp5_crtc code. The majority of the references to these params
is in code that executes after the atomic swap has occurred, so it's okay
to use crtc->state in them. There are a couple of legacy LM cursor ops that
may not use the updated state, but (I think) it's okay to live with that.

Now that we dynamically allocate a mixer to the CRTC, we can also remove
the static assignment to it in mdp5_crtc_init, and also drop the code that
skipped init-ing WB bound mixers (those will now be rejected by
mdp5_mixer_assign()).

Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>