selftest/devtool: use kernel provider instead of recipe allowing other kernel providers

selftest/devtool: use kernel provider instead of recipe allowing other kernel providers

To generalize the unit test for other kernel providers, use virtual/kernel instead
of linux-yocto, allowing to run the selftest on non-poky distros, i.e. poky-tiny.

Signed-off-by: Leonardo Sandoval <leonardo.sandoval.gonzalez@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>