drm/i915: Implement pipe CSC based limited range RGB output

HSW no longer has the PIPECONF bit for limited range RGB output.
Instead the pipe CSC unit must be used to perform that task.

The CSC pre offset are set to 0, since the incoming data is full
[0:255] range RGB, the coefficients are programmed to compress the
data into [0:219] range, and then we use either the CSC_MODE black
screen offset bit, or the CSC post offsets to shift the data to
the correct [16:235] range.

Also have to change the confiuration of all planes so that the
data is sent through the pipe CSC unit. For simplicity send the
plane data through the pipe CSC unit always, and in case full
range output is requested, the pipe CSC unit is set up with an
identity transform to pass the plane data through unchanged.

I've been told by some hardware people that the use of the pipe
CSC unit shouldn't result in any measurable increase in power
consumption numbers.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>