add ae y everage value get api

[alex-GuoGuo]

PR描述:

media_ctl 增加亮度统计获取接口

详细描述:

传入不同的pipeline id，返回当前ISP的AE亮度统计值

demo

unsigned int value = 0;
printf("%s, y everage before get: %d\n", __func__, value);
ae_y_everage_get(pipeline, &value);
printf("%s, y everage after get: %d\n", __func__, value);
return ret;

关联issue:

fix #449