pc: acpi-build: create memory hotplug IO region dynamically

pc: acpi-build: create memory hotplug IO region dynamically

it replaces a static complied in DSDT MMIO region
for memory hotplug with one created at runtime
leaving only truly static memory hotplug related
ASL bits in DSDT. And replaces template patching
of MEMORY_SLOTS_NUMBER value with ASL API created
named value.

Later it also would make easier to reuse current
ACPI memory hotplug on other targets.

Also later it would be possible to move remaining
memory hotplug ASL methods into build_ssdt() and
add all memory hotplug related AML into SSDT only
when memory hotplug is enabled, further reducing
ACPI tables blob if memory hotplug isn't used.

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>