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 22e6a2e14cb8ebcae059488cf24e778e4058c2bf.

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