LoongArch: fix CONFIG_ZONE_DMA32 not defined

LoongArch inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7PT2H

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Signed-off-by: NHongchen Zhang <zhanghongchen@loongson.cn>

arch/loongarch/Kconfig

@@ -149,6 +149,9 @@ config 32BIT
 config 64BIT
 	def_bool y
 
+config ZONE_DMA32
+	bool
+
 config USE_PERCPU_NUMA_NODE_ID
 	def_bool y
 	depends on NUMA