[Nouveau] turn the hmm migrate_vma upside down

[Christoph Hellwig]

Hi Jérôme, Ben and Jason,

below is a series against the hmm tree which starts revamping the
migrate_vma functionality.  The prime idea is to export three slightly
lower level functions and thus avoid the need for migrate_vma_ops
callbacks.

Diffstat:

    4 files changed, 285 insertions(+), 602 deletions(-)

A git tree is also available at:

    git://git.infradead.org/users/hch/misc.git migrate_vma-cleanup

Gitweb:

    http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/migrate_vma-cleanup