cpufreq: interactive governor: Fix not uniform buf filling & memory corruption

Each CPU has it's own load history buffer, but all they use shared
<history_load_index> variable, this lead to not uniform filling
of the cpu's circular buffers. Only about half of buffer is updated
during each buffer rewriting cycle that obligate governor to use
outdated data during freq tuning.

Moreover access to <history_load_index> variable is not atomic, that
create race conditions. Simultaneous increment could cause situation
where such check:

        if (++history_load_index == sampling_periods)
                history_load_index = 0;

not safe and buffer overflow will not be prevented. That will lead
to memory corruption.

To avoid such problems this patch move buffer-index variable to
<cpufreq_interactive_cpuinfo> structure, which is separate for each CPU.
Also, buffer overflow checking will be paranoidly changed.

Change-Id: I333a4462be17816372a7a57529811d87930058c0
Signed-off-by: Leonid Iziumtsev <x0153368@ti.com>