firmware: scmi: implement SCMI base protocol

firmware: scmi: implement SCMI base protocol

SCMI base protocol is mandatory according to the SCMI specification.

With this patch, SCMI base protocol can be accessed via SCMI transport
layers. All the commands, except SCMI_BASE_NOTIFY_ERRORS, are supported.
This is because U-Boot doesn't support interrupts and the current transport
layers are not able to handle asynchronous messages properly.

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>