cpufreq: interactive: Round up timer_rate to match jiffy

Timers are scheduled in unit of jiffies. Round up timer_rate so that
it matches the actual sampling period.

Change-Id: I47e666f835752528331f50b1e76784e6d67f8bcf
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>
cpufreq: interactive: Use del_timer/add_timer_on to rearm timers

Replace mod_timer_pinned() with del_timer(), add_timer_on().
mod_timer_pinned() always adds timer onto current CPU. Interactive
governor expects each CPU's timers to be running on the same CPU.
If cpufreq_interactive_timer_resched() is called from another CPU,
the timer will be armed on the wrong CPU.

Replacing mod_timer_pinned() with del_timer() and add_timer_on()
guarantees timers are still run on the right CPU even if another
CPU reschedules the timer. This would provide more flexibility
for future changes.

Change-Id: I3a10be37632afc0ea4e0cc9c86323b9783b216b1
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>