llvmpipe: pass color and depth sample strides into fragment shader.

llvmpipe: pass color and depth sample strides into fragment shader.

This just adds the interface and passes the depth and sample strides
into the fragment shader, nothing uses them yet.

Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4122>