Revert "RISC-V: Make BSS section as the last section in vmlinux.lds.S"

Revert "RISC-V: Make BSS section as the last section in vmlinux.lds.S"

At least BBL relies on the flat binaries containing all the bytes in the
actual image to exist in the file.  Before this revert the flat images
dropped the trailing zeros, which caused BBL to put its copy of the
device tree where Linux thought the BSS was, which wreaks all sorts of
havoc.  Manifesting the bug is a bit subtle because BBL aligns
everything to 2MiB page boundaries, but with large enough kernels you're
almost certain to get bitten by the bug.

While moving the sections around isn't a great long-term fix, it will at
least avoid producing broken images.

This reverts commit 01674e238957b5f6b8ff88d7378d3d07ad5c9c2e.

Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>