target-i386: Introduce generic CPUID feature compat function

Introduce x86_cpu_compat_set_features(), that can be used to set/unset
feature bits on specific CPU models for machine-type compatibility.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
target-i386: n270 can MOVBE

The Atom core (cpu name "n270" in QEMU speak) supports MOVBE. This is
needed when booting 3.8 and later linux kernels built with the MATOM
target because we require MOVBE in order to boot properly now.

Signed-off-by: Borislav Petkov <bp@suse.de>
[ehabkost: added compat code to disable MOVBE on pc-*-1.4 and older]
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>