Hide the AMD_{IBRS,IBPB,STIBP} flag from /proc/cpuinfo.  This was done
upstream as part of commit e7c587da "x86/speculation: Use
synthetic bits for IBRS/IBPB/STIBP".  That commit has already been
backported but this part was omitted.
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>