llvmpipe: get rid of unused tiled/linear logic

llvmpipe: get rid of unused tiled/linear logic

We do rendering to linear color buffers for quite some time, and since
switching to linear depth buffers all the tiled/linear logic was unused.
So get rid of (most) of it - there's still some LAYOUT_NONE things and
late allocation of resources which probably could be simplified.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>