mm: make memmap_init a proper function

mm: make memmap_init a proper function

memmap_init is sometimes a macro sometimes a function based on
__HAVE_ARCH_MEMMAP_INIT.  It is only a function on ia64.  Make memmap_init
a weak function instead, and let ia64 redefine it.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Pavel Tatashin <[email protected]>
Reviewed-by: Andrew Morton <[email protected]>
Reviewed-by: Oscar Salvador <[email protected]>
Cc: Steven Sistare <[email protected]>
Cc: Daniel Jordan <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Jérôme Glisse <[email protected]>
Cc: Souptick Joarder <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Wei Yang <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Pavel Tatashin <[email protected]>
Cc: Abdul Haleem <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Pasha Tatashin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>