acpi: x86: set enabled when composing _MAT entries

Instead of composing disabled _MAT entry and then later on
patching it to enabled for hotpluggbale CPUs in DSDT,
set it to enabled at the time _MAT entry is built.

It will allow to drop usage of packed structures in
following patches when build_madt() is switched to use
build_append_int_noprefix() API.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Message-Id: <20210924122802.1455362-24-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>