LoongArch: Enable ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS

Provide support for CONFIG_MSEAL_SYSTEM_MAPPINGS on LoongArch, covering
the vdso.

Link: https://lore.kernel.org/all/25bad37f-273e-4626-999c-e1890be96182@lucifer.local/


Acked-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Acked-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Jeff Xu <jeffxu@chromium.org>
Tested-by: Yuli Wang <wangyuli@uniontech.com>
Signed-off-by: Yuli Wang <wangyuli@uniontech.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>