mm/page_alloc.c: calc the right pfn if page size is not 4K

Previous 0x100000 is used to check the 4G limit in
find_zone_movable_pfns_for_nodes().  This is right in x86 because the page
size can only be 4K.  But 16K and 64K are available in arm64.  So replace
it with PHYS_PFN(SZ_4G).

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ma Wupeng <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Reviewed-by: Anshuman Khandual <[email protected]>
Acked-by: Ard Biesheuvel <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Ma Wupeng

mm/page_alloc.c

@@ -7821,7 +7821,7 @@ static void __init find_zone_movable_pfns_for_nodes(void)
 
 			usable_startpfn = memblock_region_memory_base_pfn(r);
 
-			if (usable_startpfn < 0x100000) {
+			if (usable_startpfn < PHYS_PFN(SZ_4G)) {
 				mem_below_4gb_not_mirrored = true;
 				continue;
 			}