drm/vc4: hdmi: Remove drm_encoder->crtc usage

The drm_encoder crtc pointer isn't really fit for an atomic driver,
let's rely on the connector state instead.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20210707141930.1811128-1-maxime@cerno.tech