PM / devfreq: Add new flag to do simple clock scaling

Add new flag "simple_scaling" to on demand governor so that
the clocks can be scaled up only when the load is more than
up threshold and can be scaled down only when the load is less
than down differential data as provided within
struct devfreq_simple_ondemand_data.

Change-Id: Ibc6ab6297c1b64b6e6eaaa76d735d0b9ae0f6477
Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>