drm/sun4i: hdmi: Replace drm_detect_hdmi_monitor() with is_hdmi

Once EDID is parsed, the monitor HDMI support information is available
through drm_display_info.is_hdmi.

This driver calls drm_detect_hdmi_monitor() to receive the same
information and stores its own cached value, which is less efficient.

Avoid calling drm_detect_hdmi_monitor() and use drm_display_info.is_hdmi
instead and also remove sun4i_hdmi.hdmi_monitor as it is no longer
necessary.

Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220421170725.903361-6-jose.exposito89@gmail.com