Fix up Sandybridge C state generation code

This code fixes the sandybridge C state generation code to work with
the current version of the ACPI code generator.

Change-Id: I56ae1185dc0694c06976236523fdcbe5c1795b01
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/950
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/arch/x86/include/arch/cpu.h

@@ -152,6 +152,7 @@ struct cpu_device_id {
 struct cpu_driver {
 	struct device_operations *ops;
 	struct cpu_device_id *id_table;
+	struct acpi_cstate *cstates;
 };
 
 struct device;