ACPI: Declare GNVS variables globally

There is a common place where acpigen generates these,
so the declarations for the OperationRegions should be
centralized too.

Change-Id: I772492ca9e651b60244c565d1e926dc2ad33cfd8
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49795
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/acpi/dsdt_top.asl b/src/acpi/dsdt_top.asl
index 853b087..761c1b5 100644
--- a/src/acpi/dsdt_top.asl
+++ b/src/acpi/dsdt_top.asl
@@ -1 +1,3 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <acpi/acpigen_extern.asl>