RISC-V nommu support v3

[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.

A git tree is available here:

    git://git.infradead.org/users/hch/riscv.git riscv-nommu.3

Gitweb:

    http://git.infradead.org/users/hch/riscv.git/shortlog/refs/heads/riscv-nommu.3

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 v2:
 - rebased to 5.3-rc
 - remove the EFI image header for nommu builds
 - set ARCH_SLAB_MINALIGN to ensure stack alignment in the flat binary
   loader
 - minor comment improvement
 - use #defines for more CSRs

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