libfdt: Activate testcase for appending properties

[Jon Loeliger]

> Commit a31e3ef83bfce62d07695355e5f06cd4d0e44b86 introduced new libfdt
> functions to append to existing properties.  It also included a test case
> for this, but neglected to update the Makefile and run_tests.sh script
> to actually build and execute this testcase.
> 
> This patch corrects the oversight.
> 
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>

Applied.  Thanks.

jdl