arm64: Add support ARCH_SUPPORTS_INT128

The gcc support __SIZEOF_INT128__ and __int128 in arm64, thus,
enable ARCH_SUPPORTS_INT128 to make mul_u64_u32_shr() a bit
more efficient in scheduler.

Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>