tinycrypt: Add test case for the ECC DH algorithm

This commit adds the test-case for the ECC DH algorithm.

Origin: https://github.com/01org/tinycrypt/tree/v0.2.0

The code was refactored to eliminate function calls and checkpatch
errors. Furthermore, the PRNG was replaced by sys_rand32_init.
 Refactoring history is available at:

Repo:       https://gitlab.com/santes/tinycrypt/tree/refactoring


Commit:     f71fc46403e90be0c54a77150e0539756d8314e7

Jira: ZEP-614
Jira: ZEP-861

Change-Id: I884f26ef8e9ff8e79ed0858678c4f51a37796e02
Signed-off-by: Flavio Santes <flavio.santes@intel.com>