sev/i386: add command to initialize the memory encryption context

When memory encryption is enabled, KVM_SEV_INIT command is used to
initialize the platform. The command loads the SEV related persistent
data from non-volatile storage and initializes the platform context.
This command should be first issued before invoking any other guest
commands provided by the SEV firmware.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/i386/sev-stub.c

@@ -0,0 +1,41 @@
+/*
+ * QEMU SEV stub
+ *
+ * Copyright Advanced Micro Devices 2018
+ *
+ * Authors:
+ *      Brijesh Singh <brijesh.singh@amd.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ *
+ */
+
+#include "qemu/osdep.h"
+#include "qemu-common.h"
+#include "sev_i386.h"
+
+SevInfo *sev_get_info(void)
+{
+    return NULL;
+}
+
+bool sev_enabled(void)
+{
+    return false;
+}
+
+uint64_t sev_get_me_mask(void)
+{
+    return ~0;
+}
+
+uint32_t sev_get_cbit_position(void)
+{
+    return 0;
+}
+
+uint32_t sev_get_reduced_phys_bits(void)
+{
+    return 0;
+}