video/exynos: dp: Move hotplug into a workqueue

video/exynos: dp: Move hotplug into a workqueue

Move the hotplug related code from probe and resume into a workqueue.
This allows us to initialize the DP driver (and resume it) when there
is no monitor connected.

BUG=chrome-os-partner:10829
BUG=chrome-os-partner:11158
BUG=chrome-os-partner:12046
TEST=Tested on snow, screen came up on power-on and resume

Change-Id: I1cd21d8430541396a376dc31c0be51a29f0560fc
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/29143
Reviewed-by: Olof Johansson <olofj@chromium.org>