The SLCLI allows only to update the firmware, but you should be able to use rest, soap, xmlrpc, python, ruby, java, go, etc., or any other supported language to retrieve this data through object-masks.
Try with the following REST call, it should retrieve the firmware information for a bare metal server:
https://[unserName]:[apiKey]@api.softlayer.com/rest/v3/SoftLayer_Hardware_Server/[baremetalID]/getObject?objectMask=mask[components[hardwareComponentModel[firmwares],revision.firmware]]
Change [unserName], [apiKey], and [baremetalID] with your own information.
For all hardware devices into the account:
https://[userName]:[apiKey]@api.softlayer.com/rest/v3/SoftLayer_Account/getHardware?objectMask=mask[id,fullyQualifiedDomainName,components[hardwareComponentModel[firmwares],revision.firmware]]
https://softlayer.github.io/reference/services/SoftLayer_Hardware_Server/getObject
https://softlayer.github.io/reference/services/SoftLayer_Hardware_Server/getComponents
https://softlayer.github.io/reference/services/SoftLayer_Account/getHardware
https://softlayer.github.io/reference/datatypes/SoftLayer_Hardware/#components
https://softlayer.github.io/reference/datatypes/SoftLayer_Hardware_Server/#components
https://softlayer.github.io/reference/datatypes/SoftLayer_Hardware_Component/