sdkext: use simpler kernel module for devtool test

sdkext: use simpler kernel module for devtool test

The current devtool test for the building of an out-of-tree kernel
module uses something which requires several "high order" kconfigs to
be set. This results in the test failing, not for expected reasons,
but rather because it depends on specific kernel configuration.

You will get error messages such as

  ERROR: "video_ioctl2"
  [.../1.0-r5/testsdkext/workspace/sources/v4l2loopback-driver/v4l2loopback.ko]
  undefined!
  ERROR: "video_unregister_device"
  [.../1.0-r5/testsdkext/workspace/sources/v4l2loopback-driver/v4l2loopback.ko]
  undefined!

Using a simpler hello-world kernel module example will only require
that CONFIG_MODULE is enabled, thus avoiding a false positive.

Signed-off-by: Mark Asselstine <mark.asselstine@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>