cpufreq: interactive: add sysfs control for timer rate

Add a new sysfs control that tunes the rate of the timer used to
increase cpu frequency

Change-Id: I1aa13ae54bb43aff5b3688984d2955f56aae1658
Signed-off-by: Allen Martin <amartin@nvidia.com>

Conflicts:
	drivers/cpufreq/cpufreq_interactive.c