firmware: scmi: install base protocol to SCMI agent

firmware: scmi: install base protocol to SCMI agent

SCMI base protocol is mandatory, and once SCMI node is found in a device
tree, the protocol handle (udevice) is unconditionally installed to
the agent. Then basic information will be retrieved from SCMI server via
the protocol and saved into the agent instance's local storage.

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>