drm/nouveau: Suspend and resume clients with client helpers

Replace calls to drm_fb_helper_set_suspend_unlocked() with calls
to the client functions drm_client_dev_suspend() and
drm_client_dev_resume(). Any registered in-kernel client will now
receive suspend and resume events.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Karol Herbst <kherbst@redhat.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Danilo Krummrich <dakr@redhat.com>
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241014085740.582287-10-tzimmermann@suse.de