tests/amdgpu: Secure bounce test (v4)

Implement secure bounce test. Steps implemented
as outlined by Christian K.

v2: Remove gpu_info; add comment describing
    the purpose and steps of the test.
v3: Parameterize "secure" in amdgpu_bo_lcopy() and
    amdgpu_bo_move(). Set them both to 0.
    Allocate buffer Bob to be non-TMZ.
v4: Fix an off-by-one bug which was causing
    the test to segfault.

Acked-by: Huang Rui <ray.huang@amd.com>
Acked-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>