drm/amdgpu: Adjust MES polling timeout for sriov

[why]
MES response time in sriov may be longer than default value
due to reset or init in other VF. A timeout value specific
to sriov is needed.

[how]
When in sriov, adjust the timeout value to calculated
worst case scenario.

Signed-off-by: Yiqing Yao <yiqing.yao@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>