drm/i915: Clear i915->display when no longer valid

drm/i915: Clear i915->display when no longer valid

Don't leave a stale i915->display pointer hanging around after
the display driver has been torn down. Apparently the gt code
calls into the reset codepaths after this, and if the display
pointer is still around we may try to access freed memory.

The whole teardown sequence here seems rather suspect. Why is
display done first and then everything else via the managed
release? Who the heck knows. Someone really needs to dig into
this stuff and figure out the proper init/cleanup sequence for
both i915 (real and mock) and xe...

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Jouni Högander <jouni.hogander@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patch.msgid.link/20260415210411.24750-2-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>