Make vmi_step_mem_event universal so it can be called with any type of e...

...vent and not just from callbacks. This is especially useful for handling INT3 events where INT3 was injected from the hypervisor and needs to be re-written into the target location after processing the trap.

This PR also expands the use of this function to multiple vCPUs for which we need to keep track how many internal singel-step events are registered as to not having to loop through the list of events to check if the MFT flag can be removed or not.