drm/amdgpu: disable concurrent flushes for Navi10 v2

Navi10 have a bug in the SDMA which can theoretically cause memory
corruption with concurrent VMID flushes

v2: explicitely check Navi10

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>