sensors: split building from manager object

To increase testability, split out the building of sensors
from the sensor manager.  And this further splits out building
from a configuration file.

Tested: Verified code continued to build and link.
Tested: Ran on quanta-q71l board and it behaved as expected.

Change-Id: Ib63a11e1107b1864c3c370bba2bd9ef2effa42f3
Signed-off-by: Patrick Venture <venture@google.com>
8 files changed