svga: fix texture buffer object regression

svga: fix texture buffer object regression

With change 8aba778fa2cd98a0b5a7429d3c5057778a0c808c we stopped binding
sampler objects for texture buffers.  That broke our texture sample /
sampler view setup code.

Now, we loop over the max(num samplers, num sampler views) and handle
the sampler and view information separately.  For texture buffers,
the sampler will be NULL but the sampler view non-null.

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