cpufreq: Add a boostpulse interface to ondemand

For applications that require a one-shot increase in frequency,
the boostpulse interface would help to scale to max for the time
specified in boostime. This helps applications that currently
increases scaling_min_freq and resets later after a fixed duration.
Instead of changing scaling_min_freq applications can directly write
to boostpulse and governer resets during regular timer after the time
expires.

Based on work by Narayanan Gopalakrishnan <nargop@codeaurora.org> with
the following changes:

Remove boostfreq tunable and set it to policy->max always
Apply a sampling down factor of 10 and make the default boost time 1 sec.
attributes sampling_rate & boostpulse to 666 mode to avoid ramdisk change.