tests/misc/llext-edk: Do run the test, instead of only building it

As commit 6a1d9877 ("cmake: Add LL_EXTENSION_BUILD to EDK flags")
made clear, only building an application with the EDK is not enough to
prevent regressions. This patch address that by also running the
application using the extension built with the EDK.

To provide a more comprehensive test, the application runs the extension
code on both kernel and user space, using a parameter sent by the
application. Assertions on the output from the application are used to
ensure expected results.

For now, tests only run on qemu_cortex_r5, but this can be expanded in
the future.

Signed-off-by: Ederson de Souza <ederson.desouza@intel.com>