dm: don't deassign pass through PCIe device in DM

Let the ACRN HV to do this in shutdown sequence. In this case, the RTVM could be
still alive if something wrong happened to cause the DM died.

Tracked-On: #4428
Signed-off-by: Li Fei1 <fei1.li@intel.com>

devicemodel/core/main.c

@@ -686,7 +686,8 @@ vm_loop(struct vmctx *ctx)
 			break;
 		}
 
-		if (VM_SUSPEND_SYSTEM_RESET == vm_get_suspend_mode()) {
+		/* RTVM can't be reset */
+		if ((VM_SUSPEND_SYSTEM_RESET == vm_get_suspend_mode()) && (!is_rtvm)) {
 			vm_system_reset(ctx);
 		}