kexec: fix build error when hugetlbfs is disabled

free_huge_page() is undefined without CONFIG_HUGETLBFS and there's no
need to filter PageHuge() page is such a configuration either, so avoid
exporting the symbol to fix a build error:

   In file included from kernel/kexec.c:14:0:
   kernel/kexec.c: In function 'crash_save_vmcoreinfo_init':
   kernel/kexec.c:1623:20: error: 'free_huge_page' undeclared (first use in this function)
     VMCOREINFO_SYMBOL(free_huge_page);
                       ^

Introduced by commit 8f1d26d ("kexec: export free_huge_page to
VMCOREINFO")

Reported-by: kbuild test robot <[email protected]>
Acked-by: Olof Johansson <[email protected]>
Cc: Atsushi Kumagai <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Vivek Goyal <[email protected]>
Cc: Andrew Morton <[email protected]>
Signed-off-by: David Rientjes <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

kernel/kexec.c

@@ -1620,7 +1620,9 @@ static int __init crash_save_vmcoreinfo_init(void)
 #endif
 	VMCOREINFO_NUMBER(PG_head_mask);
 	VMCOREINFO_NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE);
+#ifdef CONFIG_HUGETLBFS
 	VMCOREINFO_SYMBOL(free_huge_page);
+#endif
 
 	arch_crash_save_vmcoreinfo();
 	update_vmcoreinfo_note();