mm: Export static key mem_reliable

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4SK3S
CVE: NA

--------------------------------

Static key mem_reliable is used to check wheater memory reliable's status
in kernel's inline functions. These inline function rely on this but dirver
can not use because this symbol is not exported.
To slove this problem, export this symbol to make prepration for driver to
use memory reliable's inline function.
Signed-off-by: NMa Wupeng <mawupeng1@huawei.com>
Reviewed-by: NKefeng Wang <wangkefeng.wang@huawei.com>

include/linux/mem_reliable.h

@@ -10,7 +10,7 @@
 
 #ifdef CONFIG_MEMORY_RELIABLE
 
-extern struct static_key_false mem_reliable;
+DECLARE_STATIC_KEY_FALSE(mem_reliable);
 
 extern bool reliable_enabled;
 extern bool shmem_reliable;

mm/mem_reliable.c

@@ -9,6 +9,7 @@
 #include <linux/mmzone.h>
 
 DEFINE_STATIC_KEY_FALSE(mem_reliable);
+EXPORT_SYMBOL_GPL(mem_reliable);
 
 bool reliable_enabled;