arch/x86: Drop `cstates` pointer from CPU drivers

Nothing uses this pointer anymore.

Change-Id: Id2dee8f4cb243114d6f7f7485402acb9b73b7900
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49808
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

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

@@ -217,7 +217,6 @@ struct cpu_device_id {
 struct cpu_driver {
 	struct device_operations *ops;
 	const struct cpu_device_id *id_table;
-	struct acpi_cstate *cstates;
 };
 
 struct cpu_driver *find_cpu_driver(struct device *cpu);