testcases: sample testcase to generate project's documentation

This is a sample static testcase (that needs no hardware target) that
will build the documentation and ensure it builds without issues.

Change-Id: I7174205522be9aead350e67b1672b8e976cb9191
Signed-off-by: Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>