Constify struct cpu_device_id instances

There is currently no case where a struct cpu_device_id instance needs
to be modified. Thus, declare all instances as const.

Change-Id: I5ec7460b56d75d255b3451d76a46df76a51d6365
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-on: https://review.coreboot.org/22526
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/cpu/intel/model_f4x/model_f4x_init.c

@@ -47,7 +47,7 @@ static struct device_operations cpu_dev_ops = {
 	.init = model_f4x_init,
 };
 
-static struct cpu_device_id cpu_table[] = {
+static const struct cpu_device_id cpu_table[] = {
 	{ X86_VENDOR_INTEL, 0x0f41 }, /* Xeon */
 	{ 0, 0 },
 };