UBUNTU: SAUCE: reinstate MFENCE_RDTSC feature definition

CVE-2017-5753 (Spectre v1 Intel)
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

arch/x86/include/asm/cpufeatures.h

@@ -92,6 +92,7 @@
 #define X86_FEATURE_SYSCALL32	( 3*32+14) /* "" syscall in ia32 userspace */
 #define X86_FEATURE_SYSENTER32	( 3*32+15) /* "" sysenter in ia32 userspace */
 #define X86_FEATURE_REP_GOOD	( 3*32+16) /* rep microcode works well */
+#define X86_FEATURE_MFENCE_RDTSC ( 3*32+17) /* "" Mfence synchronizes RDTSC */
 #define X86_FEATURE_LFENCE_RDTSC ( 3*32+18) /* "" Lfence synchronizes RDTSC */
 /* free, was #define X86_FEATURE_11AP	( 3*32+19) * "" Bad local APIC aka 11AP */
 #define X86_FEATURE_NOPL	( 3*32+20) /* The NOPL (0F 1F) instructions */