sensor: add device config helpers

Define some configuration structures and macros that can be used in
device configuration.  These usage scenarios are as follows:

 * device drivers will use SENSOR_DECLARE_* macros in their device
   configuration structures and SENSOR_GET_* macros in the init
   functions;

 * application code will use SENSOR_TRIG_* to fill in the device
   configuration structures.

Change-Id: I3a897999175b14a4cd1111da4c26434741294e52
Signed-off-by: Vlad Dogaru <vlad.dogaru@intel.com>