amdgpu: Use drmIoctl in amdgpu_ioctl_wait_cs

This is safe now because the ioctl uses an absolute timeout.

This prevents amdgpu_cs_query_fence_status from returning early e.g.
when a signal is delivered, which in turn caused Mesa winsys code to
assume a BO was idle when it actually wasn't yet.

Reviewed-by: Christian König <christian.koenig@amd.com>