f2fs: move f2fs_xattr_handlers and f2fs_xattr_handler_map to .rodata

f2fs: move f2fs_xattr_handlers and f2fs_xattr_handler_map to .rodata

This makes it harder for accidental or malicious changes to
f2fs_xattr_handlers or f2fs_xattr_handler_map at runtime.

Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Chao Yu <chao@kernel.org>
Cc: linux-f2fs-devel@lists.sourceforge.net
Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
Link: https://lore.kernel.org/r/20230930050033.41174-11-wedsonaf@gmail.com
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>