dax, kmem: calculate abstract distance with general interface

Previously, a fixed abstract distance MEMTIER_DEFAULT_DAX_ADISTANCE is
used for slow memory type in kmem driver.  This limits the usage of kmem
driver, for example, it cannot be used for HBM (high bandwidth memory).

So, we use the general abstract distance calculation mechanism in kmem
drivers to get more accurate abstract distance on systems with proper
support.  The original MEMTIER_DEFAULT_DAX_ADISTANCE is used as fallback
only.

Now, multiple memory types may be managed by kmem.  These memory types are
put into the "kmem_memory_types" list and protected by
kmem_memory_type_lock.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: "Huang, Ying" <[email protected]>
Tested-by: Bharata B Rao <[email protected]>
Reviewed-by: Dave Jiang <[email protected]>
Reviewed-by: Alistair Popple <[email protected]>
Cc: Aneesh Kumar K.V <[email protected]>
Cc: Wei Xu <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Jonathan Cameron <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Yang Shi <[email protected]>
Cc: Rafael J Wysocki <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

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