drm/i915: Split color mgmt based on single vs. double buffered registers

drm/i915: Split color mgmt based on single vs. double buffered registers

Split the color management hooks along the single vs. double
buffered registers line. Of the currently programmed registers
GAMMA_MODE and the ilk+ pipe CSC are double buffered, the
LUTS and CHV CGM block are single buffered.

The double buffered register will be programmed during the
normal pipe update with evasion, and also during pipe enable
so that the settings will already be correct when the pipe
starts up before the planes are enabled.

The single buffered registers are currently programmed before
the vblank evade. Which is totally wrong, but we'll correct
that later.

v2: Add some docs to explain the two vfuncs (Matt,Uma)
    Rebase

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190205160848.24662-6-ville.syrjala@linux.intel.com
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>