drm/xe/guc: move guc_fini over to devm

Make sure to actually call this when the device is removed. Currently we
only trigger it when the driver instance goes away, but that doesn't
work too well with hotunplug, since device can be removed and re-probed
with a new driver instance, where the guc_fini() is called too late.
Move the fini over to devm to ensure this is called when device is
removed.

References: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/1717
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240522102143.128069-22-matthew.auld@intel.com