nouveau/dmem: evict device private memory during release

nouveau/dmem: evict device private memory during release

When the module is unloaded or a GPU is unbound from the module it is
possible for device private pages to still be mapped in currently running
processes.  This can lead to a hangs and RCU stall warnings when unbinding
the device as memunmap_pages() will wait in an uninterruptible state until
all device pages have been freed which may never happen.

Fix this by migrating device mappings back to normal CPU memory prior to
freeing the GPU memory chunks and associated device private pages.

Link: https://lkml.kernel.org/r/66277601fb8fda9af408b33da9887192bf895bda.1664366292.git-series.apopple@nvidia.com
Signed-off-by: Alistair Popple <apopple@nvidia.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Alex Sierra <alex.sierra@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>