test/amdgpu: disable bo eviction test by default

if some system has no swap space and memory is less, than the test
could fail.
And bo eviction test takes much more time in some system, which effects
automation test result and efficiency.
So disable it by default now, only be used by developer manually.

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