drm/vc4: drv: Call component_unbind_all()

While we were using the component framework to deal with all the DRM
subdevices, we were not calling component_unbind_all().

This leads to none of the subdevices freeing up their resources as part of
their unbind() or device managed hooks.

Fixes: c8b75bca ("drm/vc4: Add KMS support for Raspberry Pi.")
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>