drm/amdgpu/sdma: add flag for tracking disable_kq

For SDMA, we still need kernel queues for paging so
they need to be initialized, but we no not want to
accept submissions from userspace when disable_kq
is set.

Reviewed-by: Sunil Khatri <sunil.khatri@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>