drm/vc4: crtc: Make sure the HDMI controller is powered at boot

If vc4_crtc_disable_at_boot runs, we call into the HDMI controller hooks
to disable it but we never made sure it was running and the core clock
was running either.

This doesn't fix any known bugs, but it's still something we should make
sure of.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>