MIPS: Restore symbol versions for copy_page_cpu and clear_page_cpu

The mips build generates two warnings:

WARNING: modpost: EXPORT symbol "clear_page_cpu" [vmlinux] version generation failed, symbol will not be versioned.
WARNING: modpost: EXPORT symbol "copy_page_cpu" [vmlinux] version generation failed, symbol will not be versioned.

Add their prototypes to be defined in asm-prototypes.h, so that
genksyms knows the types of these symbols and can generate CRCs for
them.
Reported-by: k2ci <kernel-bot@kylinos.cn>
Signed-off-by: Genjian Zhang <zhanggenjian@kylinos.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/include/asm/asm-prototypes.h

@@ -6,3 +6,6 @@
 #include <linux/uaccess.h>
 #include <asm/ftrace.h>
 #include <asm/mmu_context.h>
+
+extern void clear_page_cpu(void *page);
+extern void copy_page_cpu(void *to, void *from);