cpu/intel/model_206ax: Always return a package from _CST

The _CST method is supposed to return a package. If a mainboard used
zero for all ACPI C-states, the generated _CST would return nothing,
which is invalid. Instead, return a package with no C-state entries.

This change is a no-op, since all mainboards have at least one valid
ACPI C-state. This is what `acpigen_write_CST_package()` does, too.

Change-Id: I1f531e168683ed108a8d6d03dee6f5415fd15587
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49092
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/cpu/intel/model_206ax/acpi.c

@@ -31,8 +31,6 @@ static void generate_cstate_entries(acpi_cstate_t *cstates,
 		++cstate_count;
 	if (c3 > 0)
 		++cstate_count;
-	if (!cstate_count)
-		return;
 
 	acpigen_write_package(cstate_count + 1);
 	acpigen_write_byte(cstate_count);