drm: bridge: dw-hdmi: Create connector in the bridge attach operation

The DRM device is not guaranteed by the bridge API to be available
before the attach callback. The driver performs properly at the moment
as it doesn't use the drm_bridge_add() registration method. As this will
be changed later, move connector creation to attach time to ensure
compatibility with the API.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170117082910.27023-10-laurent.pinchart+renesas@ideasonboard.com