Use the improved HMAC_PRNG test from TinyCrypt version 0.2.8,
(commit 6e0eb53fc8403988f97345e94081b0453f47231d),
that was imported into Zephyr in
commit 06d0b6a694.
Rewrote part of the test code to use the ztest asserts and
test_utils.h functionality.
Signed-off-by: Thomas Ebert Hansen <thoh@oticon.com>