pc: acpi: mark all possible CPUs as enabled in SRAT

If QEMU is started with  -numa ... Windows only notices that
CPU has been hot-added but it will not online such CPUs.

It's caused by the fact that possible CPUs are flagged as
not enabled in SRAT and Windows honoring that information
doesn't use corresponding CPU.

ACPI 5.0 Spec regarding to flag says:
"
Table 5-47 Local APIC Flags
...
Enabled: if zero, this processor is unusable, and the operating system
support will not attempt to use it.
"

Fix QEMU to adhere to spec and mark possible CPUs as enabled
in SRAT.

With that Windows onlines hot-added CPUs as expected.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>