UBUNTU: SAUCE: Set generic SSBD feature for Intel cpus

UBUNTU: SAUCE: Set generic SSBD feature for Intel cpus

The generic feature bit needs to be set for Intel and AMD CPUs
which have support. In more recent code there is a shared
function for this in arch/x86/kernel/cpu/common.c. But for the
backport we need to duplicate that code into amd.c and intel.c.

CVE-2018-3639 (x86)

Fixes: a93338c "x86/cpufeatures: Disentangle SSBD enumeration"
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>