drm/amdgpu: Enable GFX11 SDMA context empty interrupt

Enable SDMA queue empty context switching. SDMA context switch due to
quantum programming no longer done here (as of sdma v6), so re-name
sdma_v6_0_ctx_switch_enable to sdma_v6_0_ctxempty_int_enable to reflect
this.

Also program SDMAx_QUEUEx_SCHEDULE_CNTL for context switch due to
quantum in KFD. Set to amdgpu_sdma_phase_quantum (defaults to 32 i.e.
3200us).

Signed-off-by: Graham Sider <Graham.Sider@amd.com>
Reviewed-by: Harish Kasiviswanathan <Harish.Kasiviswanathan@amd.com>
Reviewed-by: Stanley Yang <Stanley.Yang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>