drm/bridge: adv7511: Switch to using drm_kms_helper_hotplug_event()

In chasing down a previous issue with EDID probing from calling
drm_helper_hpd_irq_event() from irq context, Laurent noticed
that the DRM documentation suggests that
drm_kms_helper_hotplug_event() should be used instead.

Thus this patch replaces drm_helper_hpd_irq_event() with
drm_kms_helper_hotplug_event(), which requires we update the
connector.status entry and only call _hotplug_event() when the
status changes.

Cc: David Airlie <airlied@linux.ie>
Cc: Archit Taneja <architt@codeaurora.org>
Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>
Cc: Lars-Peter Clausen <lars@metafoo.de>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1484614372-15342-3-git-send-email-john.stultz@linaro.org