iio: hid_sensor_hub: Common PM functions

To improvement power and performance, both regular and run time callbacks
are introduced. Because of auto suspend delay, two consecutive read
don't have to go through full power on/off procedure. The auto suspend
time can be adjusted using regular power attributes of PM sysfs.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>