drm/i915: Cleanup test data during long/short hotplug

Automated test data that is updated when a test is requested is not cleared
till next automated test request is recevied which can cause various
problems. This patch fixes this by clearing this during the next
short pulse and on hot unplug.

For example, when TEST_LINK_TRAINING is requested it is updated
to appropriate variable inside intel_dp_handle_test_request
but is also cleared only inside the same function. if the next
short pulse does not have the AUTOMATED_TEST_REQUEST bits set
the variable will not be cleared resulting in carrying incorrect
test status in local variables.

v2: Added comments and moved nack and defer variables before set_edid
(Sonika)

Signed-off-by: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
Signed-off-by: Shubhangi Shrivastava <shubhangi.shrivastava@intel.com>
Reviewed-by: Sonika Jindal <sonika.jindal@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>