llvmpipe: get rid of llvmpipe_get_texture_tile_linear

llvmpipe: get rid of llvmpipe_get_texture_tile_linear

Because the layout is always linear this didn't really do much any longer -
at some point this triggered per-tile swizzled->linear conversion. The x/y
coords were ignored too.
Apart from triggering conversion, this also invoked alloc_image_data(), which
could only actually trigger mapping of display target resources. So, instead
just call resource_map in the callers (which also gives the ability to unmap
again). Note that mapping/unmapping of display target resources still isn't
really all that clean (map/unmap may be unmatched, and all such mappings use
the same pointer thus usage flags are a lie).

Reviewed-by: Brian Paul <brianp@vmware.com>