boards: dts: Add fxas21002 interrupt bindings and fix sensor sample

Adds dts bindings for the fxas21002 interrupt pins to all boards that
have this sensor.

The fxas21002 driver is currently only aware of one sensor interrupt
pin, therefore the routing of INT1 or INT2 to the driver is handled in
each board's dts.fixup.

The fxas21002 sample application has been broken since the refactoring
of the mcux gpio driver to dts in commit
4e8f29f3. The sample is now fixed.

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