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/20220414101314.1250667-8-mawupeng1@huawei.com
Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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;
 			}