video/exynos: dp: Enable hotplug interrupts

video/exynos: dp: Enable hotplug interrupts

Enable hotplug interrupts and move the hotplug scheduling into the
interrupt handler. This allows us to introduce a screen at any time
while we're running.

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: I410fe3ffb9ac341a13135c09dbeb9eec8d75beef
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/29145
Reviewed-by: Olof Johansson <olofj@chromium.org>