ICL has some many planes per pipe that it is causing this test to
skip due bandwidth limitation when combined with 4K displays.

The objective of this test is test the visibility of the planes when
switching between high and low resolution, more information in the
patch that added this test 12e34d8c

 ("tests/kms_plane_lowres:
Plane visibility after atomic modesets").
So it was setting all the planes the tested pipe in the bottom left
of the display using the height of high resolution,  checking the
visibility and then switching to the low resolution mode and checking
again the visibility and now it is expected that all planes would be
invisible.

So to overcome ICL bandwidth issues, here it is testing each plane
individually.

Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>