[bazel] cleanup labels in macros to expose some externally

Some bazel macros, e.g., `opentitan_functest`, are designed to be used in external repositories, e.g. the test_hooks repository. To use these, the rules this macro (and other similar macros) instantiate must reference labels using the `@//` repository prefix. We should take a pass through this repo to determine which of these rules we want to expose externally.

CC: @cfrantz

Start by reviewing the Bazel macros, including opentitan_functest, and how they are used by the external test_hooks repository. Trace the labels referenced by these macros and determine which instantiated rules should be externally usable. Done means the intended externally exposed rules consistently use the @// repository prefix.

Written by the indexing model from the issue text.