test: dm: add protocol-specific channel test

Any SCMI protocol may have its own channel.
Test this feature on sandbox as the necessary framework was added
in a prior commit.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Etienne Carriere <etienne.carriere@foss.st.com>
2 files changed