soc/intel_adsp: soc_adsp_halt_cpu always fails when NUM_CPUS <= 1

When the target has only a single CPU, this function cannot ever
succeed. Skip all of the drama and just return -EINVAL. This makes GCC 14
happy as it doesn't get confused about possible out of bounds access of the
soc_cpus_active array.

Signed-off-by: Keith Packard <keithp@keithp.com>

Author: keith-packard

soc/intel/intel_adsp/cavs/multiprocessing.c

@@ -201,6 +201,7 @@ __imr void soc_mp_init(void)
 
 int soc_adsp_halt_cpu(int id)
 {
+#if CONFIG_MP_MAX_NUM_CPUS > 1
 	unsigned int irq_mask;
 
 	if (id == 0 || id == arch_curr_cpu()->id) {
@@ -237,4 +238,7 @@ int soc_adsp_halt_cpu(int id)
 	while ((CAVS_SHIM.pwrsts & CAVS_PWRSTS_PDSPPGS(id))) {
 	}
 	return 0;
+#else
+	return -EINVAL;
+#endif
 }