drm: bridge: dw-hdmi: Split connector creation to a separate function

Isolate all the code related to connector creation to a new
dw_hdmi_connector_create() function, to prepare for making connector
creation optional.

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/20200526011505.31884-20-laurent.pinchart+renesas@ideasonboard.com