lowRISC
Implement "Get PFM Id" and "Get PFM Supported Firmware" messages
These are defined in sections 6.22 and 6.23 of the Challenge Protocol Specification. Implementing support for them in the PA-RoT server is pending on #43, but implementing the message parsing itself can be done before that.
~~Since we would be implementing these on top of the FPM, it's unclear if we want to re-use the Cerberus message type bytes for these, or use our own until we reconcile the PFM and our FPM.~~ We implement the PFM now, so this bit is irrelevant. =)
Just to clarify the issue description, it seems that the get pfm id and get pfm supported firmware are defined in sections 6.23 and 6.24, respectively.
Began doing some work on this. There's a an issue with the spec as it requires to know what the request was in order to decode the response. If the request asks for a version id, then the response will include a 4-byte id. If the request asks for a platform id, then the response is going to be a null terminated ascii string. Talked to @mcy offline and decided that we will have to go against the spec and include an extra byte of information to distinguish the response.
