test: dm: simplify SCMI unit test on sandbox

Adding SCMI base protocol makes it inconvenient to hold the agent instance
(udevice) locally since the agent device will be re-created per each test.
Just remove it and simplify the test flows.
The test scenario is not changed at all.

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>
3 files changed