RISC-V nommu support v2

[Christoph Hellwig]

Hi all,

below is a series to support nommu mode on RISC-V.  For now this series
just works under qemu with the qemu-virt platform, but Damien has also
been able to get kernel based on this tree with additional driver hacks
to work on the Kendryte KD210, but that will take a while to cleanup
an upstream.

To be useful this series also require the RISC-V binfmt_flat support,
which I've sent out separately.

A branch that includes this series and the binfmt_flat support is
available here:

    git://git.infradead.org/users/hch/riscv.git riscv-nommu.2

Gitweb:

    http://git.infradead.org/users/hch/riscv.git/shortlog/refs/heads/riscv-nommu.2

I've also pushed out a builtroot branch that can build a RISC-V nommu
root filesystem here:

   git://git.infradead.org/users/hch/buildroot.git riscv-nommu.2

Gitweb:

   http://git.infradead.org/users/hch/buildroot.git/shortlog/refs/heads/riscv-nommu.2

Changes since v1:
 - fixes so that a kernel with this series still work on builds with an
   IOMMU
 - small clint cleanups
 - the binfmt_flat base and buildroot now don't put arguments on the stack