drm/amdgpu: For sriov reset, move IB test into exclusive mode

When put the IB test out of exclusive mode, and do sriov reset,
the IB test will randomly fail. As out of exclusive mode it uses
kiq to do read and write registers, but as it has world switch,
the kiq read and write time will be random, sometimes it will
beyond the MAX_KIQ_REG_WAIT and then the read or write register
will fail, which will result the IB test fail.

Signed-off-by: Emily Deng <Emily.Deng@amd.com>
Reviewed-by: Monk Liu <monk.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>