[4/5] x86/speculation: Add SRBDS vulnerability and mitigation documentation

[4/5] x86/speculation: Add SRBDS vulnerability and mitigation documentation

Origin: https://git.kernel.org/linus/7222a1b5b87417f22265c92deea76a6aecd0fb0f
Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2020-0543

Add documentation for the SRBDS vulnerability and its mitigation.

 [ bp: Massage.
   jpoimboe: sysfs table strings. ]

Signed-off-by: Mark Gross <mgross@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Gbp-Pq: Topic bugfix/x86/srbds
Gbp-Pq: Name 0004-x86-speculation-Add-SRBDS-vulnerability-and-mitigati.patch