Revert "llvmpipe: Use the default behavior of ALLOW_MAPPED_BUFFERS."

This reverts commit 6ec49066498097c2647d030ebe1b99a00bc38734.

This broke:
GTF-GL45.gtf21.GL3Tests.texture_lod_bias.*

not sure why but revert for now.

Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6042>
1 file changed