mm: move hot-plug specific memory init into separate functions and optimize

mm: move hot-plug specific memory init into separate functions and optimize

Combine the bits in memmap_init_zone and memmap_init_zone_device that are
related to hotplug into a single function called __memmap_init_hotplug.

Also take the opportunity to integrate __init_single_page's functionality
into this function.  In doing so we can get rid of some of the redundancy
such as the LRU pointers versus the pgmap.

Link: http://lkml.kernel.org/r/154361479366.7497.13916678539146224699.stgit@ahduyck-desk1.amr.corp.intel.com
Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Reviewed-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Tatashin <pavel.tatashin@microsoft.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>