firmware: arm_scmi: imx: Add LMM and CPU documentation

Add i.MX95 Logical Machine Management and CPU Protocol documentation.

Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Message-Id: <20250408-imx-lmm-cpu-v4-1-4c5f4a456e49@nxp.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>