svga: add VS code to set attribute W component to 1

svga: add VS code to set attribute W component to 1

There's a few 3-component vertex attribute formats that have no
equivalent SVGA3D_DECLTYPE_x format.  Previously, we had to use
the swtnl code to handle them.  This patch lets us use hwtnl for
more vertex attribute types by fetching 3-component attributes as
4-component attributes and explicitly setting the W component to 1.

This lets us handle PIPE_FORMAT_R16G16B16_SNORM/UNORM and
PIPE_FORMAT_R8G8B8_UNORM vertex attribs without using the swtnl path.

Fixes piglit normal3b3s GL_SHORT test.

Reviewed-by: Charmaine Lee <charmainel@vmware.com>