Function syscall_to_impls

pub fn syscall_to_impls<S: SyscallImpls + ?Sized>(
    impls: &S,
    n: u64,
    a0: u64,
    a1: u64,
    a2: u64,
    a3: u64,
    a4: u64,
    a5: u64,
) -> u64

This is the inverse of DefaultSyscallImpls: given a general syscall function, we map the syscalls to a SyscallImpls trait impl. This way we are taking care of the unsafe part for you, where in Rust you can just deal with SyscallImpls.