drm/i915: include some drm headers only where needed

Include drm_fourcc.h, drm_plane.h, and drm_color_mgmt.h where needed, so
we can drop the includes for drm_atomic.h and drm_fourcc.h from
i915_drv.h, reducing the build dependencies.

Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/b03711b2286396b2e9d5822f6adef4e7a6dc0f7b.1644507885.git.jani.nikula@intel.com