hw/arm/virt: Declare fwcfg as dma cache coherent in ACPI

Fw-cfg recently learned how to directly access guest memory and does so in
cache coherent fashion. Tell the guest about that fact when it's using ACPI.

Signed-off-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Shannon Zhao <shannon.zhao@linaro.org>
Message-id: 1486644810-33181-4-git-send-email-agraf@suse.de
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/arm/virt-acpi-build.c

@@ -90,6 +90,7 @@ static void acpi_dsdt_add_fw_cfg(Aml *scope, const MemMapEntry *fw_cfg_memmap)
     aml_append(dev, aml_name_decl("_HID", aml_string("QEMU0002")));
     /* device present, functioning, decoding, not shown in UI */
     aml_append(dev, aml_name_decl("_STA", aml_int(0xB)));
+    aml_append(dev, aml_name_decl("_CCA", aml_int(1)));
 
     Aml *crs = aml_resource_template();
     aml_append(crs, aml_memory32_fixed(fw_cfg_memmap->base,