drm/amdgpu: revert "add new bo flag that indicates BOs don't need fallback (v2)"

This reverts commit 6f51d28bfe8e1a676de5cd877639245bed3cc818.

Makes fallback handling to complicated. This is just a feature for the
GEM interface and shouldn't leak into the core BO create function.

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Chunming Zhou <david1.zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>