drm/amdkfd: Initialize sdma vm when creating sdma queue

This patch fixes a bug where sdma vm wasn't initialized when
an sdma queue was created in HWS mode.

This caused GPUVM faults to appear on dmesg and it is one of the
causes that SDMA queues are not working.

Signed-off-by: Xihan Zhang <xihan.zhang@amd.com>
Reviewed-by: Ben Goz <ben.goz@amd.comt>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>
Cc: stable@vger.kernel.org
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>