Revert "drm/amd/display: disable CRTCs with NULL FB on their primary plane (V2)"

This seems to cause flickering and lock-ups for a wide range of users.
Revert until we've found a proper fix for the flickering and lock-ups.

This reverts commit 36cc549d.

Cc: Shirish S <shirish.s@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>