[RFC] SVC: Timers

This PR attempts to implement the Timer kernel object.

Currently it implements CreateTimer and ClearTimer.
SetTimer and CancelTimer are not yet implemented because first we need a way to update the timers in the background while the threads wait, what would be the best way to do this?
The timer starts counting when SetTimer is called, and it awakes the waiting threads when the specified interval has passed.
I think `signaled` would be good.