amdgpu: Add memory over allocation test.

amdgpu: Add memory over allocation test.

Allocates 1 TB of memory. Test is disabled by default
since it's triggers OOM killer.

v2:
FIx the test to only alloc the BO and assert if return value
not equal to -ENOMEM and remove test disable on start.

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>