cpufreq: stats: Add 'load_table' debugfs file to show accumulated data of CPUs

cpufreq: stats: Add 'load_table' debugfs file to show accumulated data of CPUs

This patch add new 'load_table' debugfs file to show previous accumulated data
of CPUs load as following path and add CPUFREQ_LOADCHECK notification to
CPUFREQ_TRANSITION_NOTIFIER notifier chain.
- /sys/kernel/debug/cpufreq/cpuX/load_table

When governor calculates CPUs load on dbs_check_cpu(), governor send
CPUFREQ_LOADCHECK notification with CPUs load, so that cpufreq_stats
accumulates calculated CPUs load on 'load_table' storage.

This debugfs file is used to judge the correct system state or determine
suitable system resource according to current CPUs load on user-space.

This debugfs file include following data:
- Measurement point of time
- CPU frequency
- Per-CPU load

Changes since v6:
- Remove unnecessary memory free/allocation operation on
  cpufreq_stats_reset_debugfs()
- Get correct index of cpu_debugfs[] array according to cpu number
- Reset 'load_table' data when cpufreq governor is changed or updated because
  specific governor(e.g., performance/powersave) haven't used 'load_table;
  debugfs file.

Changes since v5:
- Determine index value of policy->cpu_debugfs[] according to
  cpumask_weight(policy->cpus) value
- Bug fix, store 'policy->cpu' to 'freq->cpu' before notify
  CPUFREQ_LOADCHECK notification

Changes since v4:
- Reset the data of CPUs load when cpufreq governor is changed
- Move code about creating debugfs directory to below first patch
	: [PATCH 1/2] cpufreq: Add debugfs directory for cpufreq

Changes since v3:
- Extend a range of accumulated data (10 ~ 1000)
- Add unit information of time/freq and align 'Time' field as left for readability
- Use CONFIG_CPU_FREQ_STAT depdendency instead of CONFIG_CPU_FREQ_STAT_DETATILS
- Initialize load of offline CPUx as zero(0)
- Create/remove debugfs root directory on cpufreq_stats_init/exit() because
  debugfs root is used on all CPUs.

Changes since v2:
- Code clean according to Viresh Kumar's comment
- Show both old frequency and new frequency on 'load_table' debugfs file
- Change debufs file patch as below
  old: /sys/kernel/debugfs/cpufreq/load_table
  new: /sys/kernel/debugfs/cpufreq/cpuX/load_table

Changes since v1:
- Set maximum storage size to save CPUs load on Kconfig
- Use spinlock to synchronize read/write operation for CPUs load
- Use local variable instead of global variable(struct cpufreq_freqs *freqs)
- Use pointer of data structure to get correct size of data structure
  in sizeof() macro instead of structure name
  : sizeof(struct cpufreq_freqs) -> sizeof(*stat->load_table)
- Change time unit from nanosecond to microsecond
- Remove unnecessary memory copy

Change-Id: I14e68196360a3ec00a36e7357b8c73c887abddce
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>