UPSTREAM: drm: bridge: dw-hdmi: Don't forward HPD events to DRM core before attach

UPSTREAM: drm: bridge: dw-hdmi: Don't forward HPD events to DRM core before attach

Hotplug events should only be forwarded to the DRM core by the interrupt
handler when the bridge has been attached, otherwise the DRM device
pointer will be NULL, resulting in a crash.

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/20170117082910.27023-7-laurent.pinchart+renesas@ideasonboard.com
Change-Id: Ic1387b5253d4586774cdb82e089effdd4104e380
Signed-off-by: Zheng Yang <zhengyang@rock-chips.com>
(cherry pick from ba5d7e6160b7aed4df92d1764aa90790db0e7996)