acpi/acpigen: Constify CST functions' pointers

The `acpigen_write_CST_package` and `acpigen_write_CST_package_entry`
functions don't modify the provided C-state information. So, make the
pointer parameters read-only to enforce this. Also constify arguments
where possible.

Change-Id: I9e18d82ee6c16e4435b8fad6d467e58c33194cf4
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/58391
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>

src/soc/intel/baytrail/acpi.c

@@ -28,7 +28,7 @@
 	}
 
 /* C-state map without S0ix */
-static acpi_cstate_t cstate_map[] = {
+static const acpi_cstate_t cstate_map[] = {
 	{
 		/* C1 */
 		.ctype = 1, /* ACPI C1 */