drm/amdgpu: Update NV SIMD-per-CU to 2

drm/amdgpu: Update NV SIMD-per-CU to 2

Navi series GPUs have 2 SIMDs per CU (and then 2 CUs per WGP).
The NV enum headers incorrectly listed this as 4, which later meant
we were incorrectly reporting the number of SIMDs in the HSA
topology. This could cause problems down the line for user-space
applications that want to launch a fixed amount of work to each
SIMD.

Signed-off-by: Joseph Greathouse <Joseph.Greathouse@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org