The test suite assumed that if SHA512 was enabled, then
SHA384 was also available. This is not true. There is
config MBEDTLS_SHA512_NO_SHA384 which allows precisely
to add SHA512 and not SHA384.
This commits adds the necessary `depends_on` clause,
to avoid running the SHA384 tests when config
MBEDTLS_SHA512_NO_SHA384 is set.
Signed-off-by: Cédric Meuter <cedric.meuter@gmail.com>