svga: fix shadow comparison failures

svga: fix shadow comparison failures

In some cases, We do shadow comparison cases in the fragment shader
instead of with texture sampler state.  But when we do so, we must
disable the shadow comparison test in the sampler state.  As it
was, we were doing the comparison twice, which resulted in nonsense.
Also, we had the texcoord and texel value swapped in the comparison
instruction.

Fixes about 38 Piglit tex-miplevel-selection tests.

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