QVM API clean up

Make cgame and game QVMs use cg_syscalls.c and g_syscalls.c like DLLs.
Separate QVM specific system calls (that are shared by both cgame and game) into VM_QvmSystemCall.
Put QVM-only system calls into code/game/bg_syscalls.asm
Added CVUU2 to q3asm opstrings to fix compile-error for game system call returning "unsigned short int".

QVMs can now only directly call qvmTraps_t. TRAP_SYSCALL allows running per-VM system calls.