firmware: arm_scmi: Add power management operations to SCMI bus

Introduce suspend and resume power management callbacks for `scmi_bus_type`,
modeled after `platform_pm_ops`. This enables SCMI devices on the bus to
implement their own suspend and resume behavior, allowing for more
fine-grained power control at the device level.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Message-Id: <20250704-scmi-pm-v2-1-9316cec2f9cc@nxp.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>