drm/i915: add intel_ddi_set_pipe_settings

In theory, all the DDI pipe settings should be set here, including
timing and M/N registers. For now, let's just set the DP MSA
attributes.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
[danvet: fixed up the unused typo in a #define, spotted by Jani
Nikula.]
Reviewed-by: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>