Partially undoes 61024aa1.

We may want to be able to return an existing BO from
context->ops->map_upload_bo(), in which case it is structurally awkward to
request a specific memory layout. We may also want to give map_upload_bo() the
freedom to allocate either a new (smaller) BO, or use an existing (larger) one,
for partial uploads.
Signed-off-by: Zebediah Figura <zfigura@codeweavers.com>
Signed-off-by: Henri Verbeet <hverbeet@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>