Inter-process communication mechanism for Tock.
This is a special syscall driver that allows userspace applications to share memory.
The IPC mechanism struct. NUM_UPCALLS should always equal NUM_PROCS + 1. The extra upcall is so processes can register as a service. Once const_evaluatable_checked is stable we will not need two separate const generic parameters.
Enum to mark which type of upcall is scheduled for the IPC mechanism.