target-i386: Remove ABM from qemu64 CPU model

target-i386: Remove ABM from qemu64 CPU model

ABM is not available on Sandy Bridge and older, and we want to make the
default CPU runnable in most hosts, so it won't be enabled by default in
KVM mode.

We should eventually have all features supported by TCG enabled by
default in TCG mode, but as we don't have a good mechanism today to
ensure we have different defaults in KVM and TCG mode, disable ABM in
the qemu64 CPU model entirely.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>