firmware: arm_scpi: Fix kernel doc warnings

Kernel doc validation script is unhappy and complains with the below set
of warnings.

 | Function parameter or member 'device_domain_id' not described in 'scpi_ops'
 | Function parameter or member 'get_transition_latency' not described in 'scpi_ops'
 | Function parameter or member 'add_opps_to_device' not described in 'scpi_ops'
 | Function parameter or member 'sensor_get_capability' not described in 'scpi_ops'
 | Function parameter or member 'sensor_get_info' not described in 'scpi_ops'
 | Function parameter or member 'sensor_get_value' not described in 'scpi_ops'
 | Function parameter or member 'device_get_power_state' not described in 'scpi_ops'
 | Function parameter or member 'device_set_power_state' not described in 'scpi_ops'

Fix them adding appropriate documents or missing keywords.

Link: https://lore.kernel.org/r/20210712130801.2436492-1-sudeep.holla@arm.com
Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>