CVE-2018-3639 (x86)

Add the CPU feature bit CPUID.7.0.EDX[31] which indicates whether the CPU
supports Reduced Data Speculation.

[ tglx: Split it out from a later patch ]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>

[juergh: Use word 16 instead of 18.]
Signed-off-by: Juerg Haefliger <juergh@canonical.com>