ACPI: Clean up GNVS initialisation

With the common <soc/nvs.h> approach platform does not
need to implement the common accessors or sizeof() function.

Change-Id: I1050a252f765c763c1ae2d1610cbfb0d973ba026
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49793
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/acpi/acpi.c

@@ -1473,7 +1473,8 @@ unsigned long write_acpi_tables(unsigned long start)
 
 		acpigen_set_current((char *) current);
 
-		acpi_fill_gnvs();
+		if (CONFIG(ACPI_SOC_NVS))
+			acpi_fill_gnvs();
 
 		for (dev = all_devices; dev; dev = dev->next)
 			if (dev->ops && dev->ops->acpi_inject_dsdt)