Add the missing symbol to fix build halt on aarch64 targets:
```
Contiguous PTE mappings for user memory (ARM64_CONTPTE) [Y/n/?] (NEW) make[7]: *** [scripts/kconfig/Makefile:85: syncconfig] Error 1
make[6]: *** [Makefile:686: syncconfig] Error 2
```
Signed-off-by: Shiji Yang <yangshiji66@outlook.com>
Link: https://github.com/openwrt/openwrt/pull/20954
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
de1b8012fe