powerpc/mm: Always update max/min_low_pfn in mem_topology_setup()

For both CONFIG_NUMA enabled/disabled use mem_topology_setup() to
update max/min_low_pfn.

This also adds min_low_pfn update to CONFIG_NUMA which was initialized
to zero before. (mpe: Though MEMORY_START is == 0 for PPC64=y which is
all possible NUMA=y systems)
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220704063851.295482-1-aneesh.kumar@linux.ibm.com

arch/powerpc/mm/numa.c

@@ -1160,6 +1160,9 @@ void __init mem_topology_setup(void)
 {
 	int cpu;
 
+	max_low_pfn = max_pfn = memblock_end_of_DRAM() >> PAGE_SHIFT;
+	min_low_pfn = MEMORY_START >> PAGE_SHIFT;
+
 	/*
 	 * Linux/mm assumes node 0 to be online at boot. However this is not
 	 * true on PowerPC, where node 0 is similar to any other node, it
@@ -1204,9 +1207,6 @@ void __init initmem_init(void)
 {
 	int nid;
 
-	max_low_pfn = memblock_end_of_DRAM() >> PAGE_SHIFT;
-	max_pfn = max_low_pfn;
-
 	memblock_dump_all();
 
 	for_each_online_node(nid) {