Initially all the SPEC_CTRL related bits were added to the scattered
feature word and that was used to sync between host and guest.
But now upstream has extended the feature words and moved all related
bits there. Because of that we have to change the handler code as well.

CVE-2018-3639 (x86)

[smb: tracked in private lp 1772146]
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>