KVM/VMX: Expose SSBD properly to guests

The X86_FEATURE_SSBD is an synthetic CPU feature - that is
it bit location has no relevance to the real CPUID 0x7.EBX[31]
bit position. For that we need the new CPU feature name.

Fixes: 52817587 ("x86/cpufeatures: Disentangle SSBD enumeration")
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: kvm@vger.kernel.org
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: stable@vger.kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lkml.kernel.org/r/20180521215449.26423-2-konrad.wilk@oracle.com