hw/arm/virt-acpi-build: Basic framework for building ACPI tables on ARM

Introduce a preliminary framework in virt-acpi-build.c with the main
ACPI build functions. It exposes the generated ACPI contents to
guest over fw_cfg.

The required ACPI v5.1 tables for ARM are:
- RSDP: Initial table that points to XSDT
- RSDT: Points to FADT GTDT MADT tables
- FADT: Generic information about the machine
- GTDT: Generic timer description table
- MADT: Multiple APIC description table
- DSDT: Holds all information about system devices/peripherals, pointed by FADT

Signed-off-by: Shannon Zhao <zhaoshenglong@huawei.com>
Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Message-id: 1432522520-8068-5-git-send-email-zhaoshenglong@huawei.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
