drm/amd/pm: enable pm sysfs write for one VF mode

[why]
pm sysfs should be writable in one VF mode as is in passthrough

[how]
do not remove write access on pm sysfs if device is in one VF mode

Fixes: 11c9cc95 ("amdgpu/pm: Make sysfs pm attributes as read-only for VFs")
Signed-off-by: Yiqing Yao <yiqing.yao@amd.com>
Reviewed-by: Monk Liu <Monk.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>