hv: reset per cpu sbuf pointers during vcpu reset

When shutting down SOS VM, the shared sbuf is released from guest OS, but
the per cpu sbuf pointers in hypervisor keep inact. This creates a problem
that after SOS is re-launched, hypervisor could write to the shared
buffer that no longer exists.

This patch implements sbuf_reset() and call it from reset_vcpu() to
reset sbuf pointers.

Tracked-On: #2700
Signed-off-by: Zide Chen <zide.chen@intel.com>
Acked-by: Anthony Xu <anthony.xu@intel.com>

hypervisor/release/sbuf.c

@@ -0,0 +1,10 @@
+/*
+ * Copyright (C) 2019 Intel Corporation. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <types.h>
+#include <sbuf.h>
+
+void sbuf_reset(__unused uint16_t pcpu_id) {}