input: sensors: add batch and flush interface for sensor class

Batch interface allow sensor events reported in batches, flush
interface is used to flush sensor FIFO. These two interface can
save device power by reduce the amount of device wakeup.
Sensor class provide generic interfaces for sensor drivers to access
by sensor HAL, drivers using sensors class should register corresponding
sensor class callback to export their interface.

Change-Id: I1307d731793dbc9a6a2b07de3b1de5188d0d8504
Signed-off-by: Bingzhe Cai <bingzhec@codeaurora.org>