drm/i915/dsi: Remove ->mode_set callback
drm/i915/dsi: Remove ->mode_set callback

Looking at our current dsi driver I note that:
- We don't have any slave driver right now.
- There's zero support for the hardware state readout and cross check
  code.
- All the modeset state seems to be tracked in the intel_dsi structure
  instead of the pipe config.

Given all that I can't properly audit the dsi ->mode_set callback. So
just do it as the first thing in the ->pre_pll_enable hook and hope
for the best.

Reviewed-by: Imre Deak <fbd5edba1988036c8923f0cca0cce6ac4811db29@intel.com>
Signed-off-by: Daniel Vetter <c1b6782c4af8f0673da8923a0702a1832e5940f4@ffwll.ch>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs