drm/bridge: adv7511: Enable connector polling when no interrupt is specified

Fall back to polling the connector for connect and disconnect events when
no interrupt is specified. Otherwise these events will not be noticed and
monitor hotplug does not work.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Tested-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20170905121018.11477-3-lars@metafoo.de