cpufreq: interactive: reduce chance of zero time delta on load eval

Reschedule load sampling timer after timestamp of sample start taken,
hold spinlock across entire sequence to avoid preemption.  Avoid the
WARN for zero time delta in the load sampling timer function.

Signed-off-by: Todd Poynor <toddpoynor@google.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
cpufreq: interactive: avoid underflow on active time calculation

Check for idle time delta less than elapsed time delta, avoid
underflow computing active time.

Signed-off-by: Minsung Kim <ms925.kim@samsung.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>