util: kernel: Add cpu utilization helper function

util: kernel: Add cpu utilization helper function

Add cpu utilization helper function as following:

[Detailed description of cpu utilization helper function]
int kernel_get_avg_cpu_util(struct cpu_util_data *avg_cpu)
: Store the average cpu utilization of all cpus to 'avg_cpu'

int kernel_get_per_cpu_util(struct cpu_util_data *cpus, int num_possible_cpus,
			    int *num_online_cpus);
: Store the per-cpu utilization datas to 'cpus' and store the number of
online to 'num_online_cpus'

Change-Id: I1594dc656759194ffa9468ed6eebbc159a47e5fd
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>