MIPS: loongsoon64: Reserve memory below starting pfn to prevent Oops

The cause of the problem is as follows:
1. when cat /sys/devices/system/memory/memory0/valid_zones,
   test_pages_in_a_zone() will be called.
2. test_pages_in_a_zone() finds the zone according to stat_pfn = 0.
   The smallest pfn of the numa node in the mips architecture is 128,
   and the page corresponding to the previous 0~127 pfn is not
   initialized (page->flags is 0xFFFFFFFF)
3. The nid and zonenum obtained using page_zone(pfn_to_page(0)) are out
   of bounds in the corresponding array,
   &NODE_DATA(page_to_nid(page))->node_zones[page_zonenum(page)],
   access to the out-of-bounds zone member variables appear abnormal,
   resulting in Oops.
Therefore, it is necessary to keep the page between 0 and the minimum
pfn to prevent Oops from appearing.

Signed-off-by: zhanglianjie <zhanglianjie@uniontech.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/loongson64/numa.c

@@ -129,6 +129,9 @@ static void __init node_mem_init(unsigned int node)
 		if (node_end_pfn(0) >= (0xffffffff >> PAGE_SHIFT))
 			memblock_reserve((node_addrspace_offset | 0xfe000000),
 					 32 << 20);
+
+		/* Reserve pfn range 0~node[0]->node_start_pfn */
+		memblock_reserve(0, PAGE_SIZE * start_pfn);
 	}
 }