CHROMIUM: drm/exynos: dp: Add force_connected flag

CHROMIUM: drm/exynos: dp: Add force_connected flag

Add a new flag to the DisplayPort platform data to optionally force
is_connected to return true. This is useful for cases such as ours where
we don't have a proper DP monitor connected, but rather a noisy bridge
that doesn't know when it's actually ready to assert hotplug.

This will also prevent drm from assuming we're disconnected and detaching
our encoder from the connector (thus losing us forever as a result of
the interrupt scheme in the driver, which needs to be fixed).

BUG=chromium-os:38006
TEST=Tested manually using Doug's reproduction instructions in c17 on the bug

Change-Id: If2034458d9de93259e92a0f3eb8f386c340b0d7d
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/42042
Reviewed-by: Doug Anderson <dianders@chromium.org>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>