drm/i915: remove a couple of superfluous i915_drm.h includes

Remove a couple of unnecessary includes.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230117123856.2271720-1-jani.nikula@intel.com