drm/vblank: Register drmm cleanup action once per drm_vblank_crtc

Since we'll be allocating resources for kthread_create_worker() in the
next commit (which could fail and require us to clean up the mess),
let's simplify the cleanup process a bit by registering a
drm_vblank_init_release() action for each drm_vblank_crtc so they're
still cleaned up if we fail to initialize one of them.

Changes since v3:
* Use drmm_add_action_or_reset() - Daniel Vetter

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: dri-devel@lists.freedesktop.org
Cc: nouveau@lists.freedesktop.org
Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Acked-by: Dave Airlie <airlied@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200627194657.156514-2-lyude@redhat.com