drm/meson: encoder_cvbs: switch to bridge with ATTACH_NO_CONNECTOR

Drop the local connector and move all callback to bridge funcs in order
to leverage the generic CVBS display connector.

This will also permit adding custom cvbs connectors for ADC based HPD
detection on some Amlogic SoC based boards.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
[narmstrong: fixed diplay typo in commit log]
Link: https://patchwork.freedesktop.org/patch/msgid/20211020123947.2585572-7-narmstrong@baylibre.com