PM: EM: Fix potential division-by-zero error in em_compute_costs()

In the Linux kernel, the following vulnerability has been resolved:

PM: EM: Fix potential division-by-zero error in em_compute_costs()

When the device is of a non-CPU type, table[i].performance won't be initialized in the previous em_init_performance(), resulting in division by zero when calculating costs in em_compute_costs().

Since the 'cost' algorithm is only used for EAS energy efficiency calculations and is currently not utilized by other device drivers, we should add the _is_cpu_device(dev) check to prevent this division-by-zero issue.