x86/bugs: Add AMD's variant of SSB_NO

x86/bugs: Add AMD's variant of SSB_NO

The AMD document outlining the SSBD handling
124441_AMD64_SpeculativeStoreBypassDisable_Whitepaper_final.pdf
mentions that the CPUID 8000_0008.EBX[26] will mean that the
speculative store bypass disable is no longer needed.

A copy of this document is available at:
    https://bugzilla.kernel.org/show_bug.cgi?id=199889

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>
Cc: kvm@vger.kernel.org
Cc: andrew.cooper3@citrix.com
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Link: https://lkml.kernel.org/r/20180601145921.9500-2-konrad.wilk@oracle.com