[Nouveau] dev_pagemap related cleanups v4

[Christoph Hellwig]

Hi Dan, Jérôme and Jason,

below is a series that cleans up the dev_pagemap interface so that
it is more easily usable, which removes the need to wrap it in hmm
and thus allowing to kill a lot of code

Note: this series is on top of Linux 5.2-rc6 and has some minor
conflicts with the hmm tree that are easy to resolve.

Diffstat summary:

 34 files changed, 379 insertions(+), 1016 deletions(-)

Git tree:

    git://git.infradead.org/users/hch/misc.git hmm-devmem-cleanup.4

Gitweb:

    http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/hmm-devmem-cleanup.4


Changes since v3:
 - pull in "mm/swap: Fix release_pages() when releasing devmap pages" and
   rebase the other patches on top of that
 - fold the hmm_devmem_add_resource into the DEVICE_PUBLIC memory removal
   patch
 - remove _vm_normal_page as it isn't needed without DEVICE_PUBLIC memory
 - pick up various ACKs

Changes since v2:
 - fix nvdimm kunit build
 - add a new memory type for device dax
 - fix a few issues in intermediate patches that didn't show up in the end
   result
 - incorporate feedback from Michal Hocko, including killing of
   the DEVICE_PUBLIC memory type entirely

Changes since v1:
 - rebase
 - also switch p2pdma to the internal refcount
 - add type checking for pgmap->type
 - rename the migrate method to migrate_to_ram
 - cleanup the altmap_valid flag
 - various tidbits from the reviews