drm/tegra: dpaux: Support monitor hotplugging

The dpaux driver has a quirk built-in that will delay initialization of
the display driver for a short while, trying to detect an eDP panel. The
reason for this quirk is that the panel may not report as connected
until after the display driver has initialized, at which point the fbdev
emulation will have fallen back to 1024x768 as default resolution, which
will likely not be the eDP panel's native resolution.

With upcoming DisplayPort support, the code needs to be able to cope
with hotpluggable monitors as well. Waiting for a panel to show up is no
longer going to work because the monitor may not be attached on boot. If
the output runs in DisplayPort mode, skip waiting for the panel to show
up.

Signed-off-by: Thierry Reding <treding@nvidia.com>