arm64: mm: Fix build error with CONFIG_SPARSEMEM_VMEMMAP disabled

This fix the below build error:

arch/arm64/mm/dump.c: In function ‘ptdump_init’:
arch/arm64/mm/dump.c:331:18: error: ‘VMEMMAP_START_NR’ undeclared (first use in this function)
  address_markers[VMEMMAP_START_NR].start_address =
                  ^
arch/arm64/mm/dump.c:331:18: note: each undeclared identifier is reported only once for each
function it appears in
arch/arm64/mm/dump.c:333:18: error: ‘VMEMMAP_END_NR’ undeclared (first use in this function)
  address_markers[VMEMMAP_END_NR].start_address =
                  ^
Acked-by: NLaura Abbott <labbott@redhat.com>
Signed-off-by: NJungseung Lee <js07.lee@gmail.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm64/mm/dump.c

@@ -328,10 +328,12 @@ static int ptdump_init(void)
 			for (j = 0; j < pg_level[i].num; j++)
 				pg_level[i].mask |= pg_level[i].bits[j].mask;
 
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
 	address_markers[VMEMMAP_START_NR].start_address =
 				(unsigned long)virt_to_page(PAGE_OFFSET);
 	address_markers[VMEMMAP_END_NR].start_address =
 				(unsigned long)virt_to_page(high_memory);
+#endif
 
 	pe = debugfs_create_file("kernel_page_tables", 0400, NULL, NULL,
 				 &ptdump_fops);