sb and soc: Enforce correct offset of member "chromeos" in global_nvs_t

The padding has recently been broken in commit 90ebf96df5
("soc/intel/skylake: Add GNVS variables and include SGX ASL") and fixed
again in commit af88398887 ("soc/intel/skylake: Fix broken GNVS offset
for chromeos").  Avoid this bug in the future.

Change-Id: I1bf3027bba239c8747ad26a3130a7e047d3b8c94
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-on: https://review.coreboot.org/22229
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/southbridge/intel/ibexpeak/nvs.h

@@ -14,9 +14,11 @@
  * GNU General Public License for more details.
  */
 
+#include <commonlib/helpers.h>
 #include <compiler.h>
 #include "vendorcode/google/chromeos/gnvs.h"
-typedef struct {
+
+typedef struct global_nvs_t {
 	/* Miscellaneous */
 	u16	osys; /* 0x00 - Operating System */
 	u8	smif; /* 0x02 - SMI function call ("TRAP") */
@@ -150,6 +152,7 @@ typedef struct {
 	/* ChromeOS specific (starts at 0x100)*/
 	chromeos_acpi_t chromeos;
 } __packed global_nvs_t;
+check_member(global_nvs_t, chromeos, 0x100);
 
 #ifdef __SMM__
 /* Used in SMM to find the ACPI GNVS address */