The vc4_hdmi_encoder struct was used exclusively to cache the value
returned by drm_detect_hdmi_monitor() in order to avoid calling it
multiple times.

Now that drm_detect_hdmi_monitor() has been replaced with
drm_display_info.is_hdmi, there is no need to have an extra struct.

Remove vc4_hdmi_encoder.
Signed-off-by: NJosé Expósito <jose.exposito89@gmail.com>
Signed-off-by: NMaxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220420114500.187664-3-jose.exposito89@gmail.com