drm/amdgpu: Correct and simplify sdma 4.x irq.num_types

Correct and init the sdma4.x irq.num_types.

v2: squash in fix (Alex)

Signed-off-by: Feifei Xu <Feifei.Xu@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>