Blender Git Loki

Cycles: avoid copying vertex normals attribute twice to the devices

Vertex normals are needed for normals maps and therefore are packed and send
to the device alongside the other float3 attributes. However, we already pack
and send vertex normals through `DeviceScene.tri_vnormal`.

This removes the packing of vertex normals from the attributes buffer, and
reuses `tri_vnormal` in the kernel for normals lookup for normal maps, which
reduces memory usage a bit, and speeds up device updates.

This also fixes potential missing normals updates following rB12a06292af86,
since the need for vertex normals for normals maps was overlooked.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D12237