Revert "drm/i915: Drop has_rc6 from device info"

This reverts commit 218076ab

.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Acked-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220519090802.1294691-7-tvrtko.ursulin@linux.intel.com