pc: Create pc_compat_2_1() functions

We will need new compat code for the 2.1 machine-types.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
target-i386: Rename KVM auto-feature-enable compat function

The x86_cpu_compat_disable_kvm_features() name was a bit confusing, as
it won't forcibly disable the feature for all CPU models (i.e. add it to
kvm_default_unset_features), but it will instead turn off the KVM
auto-enabling of the feature (i.e. remove it from kvm_default_features),
meaning the feature may still be enabled by default in some CPU models).

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>