drm/amdgpu: Disallow partition query during reset

Reject queries to get current partition modes during reset. Also, don't
accept sysfs interface requests to switch compute partition mode while
in reset.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Asad Kamal <asad.kamal@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>