This was fixed in initialize_cpsch before, but not in initialize_nocpsch.
Factor sdma bitmap initialization into a helper function to apply the
correct implementation in both cases without duplicating it.

v2: Added a range check
Reported-by: NEllis Michael <ellis@ellismichael.com>
Signed-off-by: NFelix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: NGraham Sider <Graham.Sider@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>