drm/amdgpu/sriov: give 8s for recover vram under RUNTIME

Extend the timeout for recovering vram bos from shadows on sr-iov
to cover the worst case scenario for timeslices and VFs

Under runtime, the wait fence time could be quite long when
other VFs are in exclusive mode. For example, for 4 VF, every
VF's exclusive timeout time is set to 3s, then the worst case is
9s. If the VF number is more than 4,then the worst case time will
be longer.
The 8s is the test data, with setting to 8s, it will pass the TDR
test for 1000 times.

SWDEV-161490

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