List of things to change in the VMM source code once Microkit has support for guests to have multiple TCBs/VCPUs.

• Most of the fault handling is already setup to take in vcpu_id, right now they're all just given GUEST_VCPU_ID since there is only one VCPU that each VMM has to handle.
• We would have to adapt guest_start and guest_restart for multiple VCPUs. We would also have to change the PSCI handling to turn on non-boot VCPUs.
• vgic_init needs to be slightly modified to set the state depending on the number of VCPUs.
• For GICv3 platforms would have to fix up the driver slightly.
• The VMM would have to have knowledge of how many VCPUs is the guest using, which is currently hard-coded but it should come from the build process by looking some kind of system description (whether the XML seL4CP system description or some higher level one, I'm not sure yet).