KVM: VMX: Introduce exit reason for receiving INIT signal on guest-mode

According to Intel SDM section 25.2 "Other Causes of VM Exits",
When INIT signal is received on a CPU that is running in VMX
non-root mode it should cause an exit with exit-reason of 3.
(See Intel SDM Appendix C "VMX BASIC EXIT REASONS")

This patch introduce the exit-reason definition.
Reviewed-by: Bhavesh Davda <bhavesh.davda@oracle.com>
Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Co-developed-by: Nikita Leshenko <nikita.leshchenko@oracle.com>
Signed-off-by: Nikita Leshenko <nikita.leshchenko@oracle.com>
Signed-off-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/uapi/asm/vmx.h

@@ -31,6 +31,7 @@
 #define EXIT_REASON_EXCEPTION_NMI       0
 #define EXIT_REASON_EXTERNAL_INTERRUPT  1
 #define EXIT_REASON_TRIPLE_FAULT        2
+#define EXIT_REASON_INIT_SIGNAL			3
 
 #define EXIT_REASON_PENDING_INTERRUPT   7
 #define EXIT_REASON_NMI_WINDOW          8
@@ -90,6 +91,7 @@
 	{ EXIT_REASON_EXCEPTION_NMI,         "EXCEPTION_NMI" }, \
 	{ EXIT_REASON_EXTERNAL_INTERRUPT,    "EXTERNAL_INTERRUPT" }, \
 	{ EXIT_REASON_TRIPLE_FAULT,          "TRIPLE_FAULT" }, \
+	{ EXIT_REASON_INIT_SIGNAL,           "INIT_SIGNAL" }, \
 	{ EXIT_REASON_PENDING_INTERRUPT,     "PENDING_INTERRUPT" }, \
 	{ EXIT_REASON_NMI_WINDOW,            "NMI_WINDOW" }, \
 	{ EXIT_REASON_TASK_SWITCH,           "TASK_SWITCH" }, \