samples: sensor: Refactor fxos8700 tests for accel-only boards

The frdm-kl25z, bbc_microbit, and reel_board have an mma8xxx
accelerometer and therefore must use the fxos8700 driver in
accelerometer-only mode instead of hybrid mode. Refactor these boards
into a separate test that uses the prj_accel.conf configuration as
described in README.rst.

Signed-off-by: Maureen Helm <maureen.helm@nxp.com>
1 file changed