cpufreq: ondemand: Change the calculation of target frequency

Ondemand calculates load in terms of frequency and increases it only
if the load_freq is greater than up_threshold multiplied by current
or average frequency. This seems to produce oscillations of frequency
between min and max because, for example, a relatively small load can
easily saturate minimum frequency and lead the CPU to max. Then, the
CPU will decrease back to min due to a small load_freq.

This patch changes the calculation method of load and target frequency
considering 2 points:
- Load computation should be independent from current or average
measured frequency. For example an absolute load 80% at 100MHz is not
necessarily equivalent to 8% at 1000MHz in the next sampling interval.
- Target frequency should be increased to any value of frequency table
proportional to absolute load, instead to only the max. Thus:

Target frequency = C * load

where C = policy->cpuinfo.max_freq / 100

Tested on Intel i7-3770 CPU @ 3.40GHz and on Quad core 1500MHz Krait.
Phoronix benchmark of Linux Kernel Compilation 3.1 test shows an
increase ~1.5% in performance. cpufreq_stats (time_in_state) shows
that middle frequencies are used more, with this patch. Highest
and lowest frequencies were used less by ~9%

Signed-off-by: Stratos Karafotis <stratosk@semaphore.gr>
cpufreq: Remove unused APERF/MPERF support

Calculation of target frequency in ondemand governor changed and it is
independent from measured average frequency.

Remove unused APERF/MPERF support.

Signed-off-by: Stratos Karafotis <stratosk@semaphore.gr>
cpufreq: Remove unused function __cpufreq_driver_getavg

Calculation of target frequency in ondemand governor changed and it is
independent from measured average frequency.

Remove unused__cpufreq_driver_getavg function and getavg member from
cpufreq_driver struct.

Signed-off-by: Stratos Karafotis <stratosk@semaphore.gr>