drm/radeon/kms: bail early for eDP in hotplug callback

Don't try and en/disable the port as it may be a hpd event from
powering up/down the panel during a modeset or dpms.

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>