acpi: introduce AML composer aml_append()

acpi: introduce AML composer aml_append()

Adds for dynamic AML creation, which will be used
for piecing ASL/AML primitives together and hiding
from user/caller details about how nested context
should be closed/packed leaving less space for
mistakes and necessity to know how AML should be
encoded, allowing user to concentrate on ASL
representation instead.

For example it will allow to create AML like this:

init_aml_allocator();
...
Aml *scope = aml_scope("PCI0")
Aml *dev = aml_device("PM")
    aml_append(dev, aml_name_decl("_ADR", aml_int(addr)))
aml_append(scope, dev);
...
free_aml_allocator();

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>