drm/i915: Add a retry counter for hotplug detect retries

On TypeC connectors we need to retry the detection after hotplug events
for a longer time, so add a retry counter to support this. The next
patch will add detection retries on TypeC ports needing this.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200330095425.29113-1-imre.deak@intel.com