drm: bridge: dw-hdmi: Make connector creation optional

Implement the drm_bridge_funcs .detect() and .get_edid() operations, and
call drm_bridge_hpd_notify() notify to report HPD. This provides the
necessary API to support disabling connector creation, do so by
accepting DRM_BRIDGE_ATTACH_NO_CONNECTOR in dw_hdmi_bridge_attach().

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200526011505.31884-23-laurent.pinchart+renesas@ideasonboard.com