tests: add macro for generating function enter log message

tests: add macro for generating function enter log message

The test-tpm2 test multiplexes a bunch of tests from a single
entrypoint test that creates the TPM2 connection. This means we only get
the nice log output which test we are looking for once for the
entrypoint.

Let's add a macro that allows it to nicely generate it for the inner
tests too and use it.