mm: add zone device coherent type memory support

Device memory that is cache coherent from device and CPU point of view. 
This is used on platforms that have an advanced system bus (like CAPI or
CXL).  Any page of a process can be migrated to such memory.  However, no
one should be allowed to pin such memory so that it can always be evicted.

[[email protected]: rebased ontop of the refcount changes, remove is_dev_private_or_coherent_page]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Alex Sierra <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
Acked-by: Felix Kuehling <[email protected]>
Reviewed-by: Alistair Popple <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Jerome Glisse <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Ralph Campbell <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

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