drm/i915/display: switch to struct drm_device based pcode interface

drm/i915/display: switch to struct drm_device based pcode interface

With the struct drm_device based pcode interface in place in both i915
and xe, we can switch display code to use that, and ditch a number of
struct drm_i915_private uses. Also drop the dependency on i915_drv.h
from a couple of files.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://lore.kernel.org/r/f948fad1b8208522e15140692c17cf493ef305d9.1750678991.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>