The recipes-rt recipes provide package and image recipes for using and testing
the PREEMPT_RT kernel. The core-image-rt*.bb images are minimal images with
a couple extra packages, including rt-tests. In order to build the image with
the linux-yocto-rt kernel, be sure to include the following line in your
local.conf, bblayers.conf, or your $MACHINE.conf.

PREFERRED_PROVIDER_virtual/kernel = "linux-yocto-rt"

If you are creating a new BSP which should use linux-yocto-rt by default,
use the line above in the $MACHINE.conf in your BSP layer, and specify the
following in a linux-yocto-rt bbappend recipe:

COMPATIBLE_MACHINE:$MACHINE = $MACHINE