`spd` command is currently very Gimlet-specific

[cbiffle]

Currently, the spd command relies on the existence of a gimlet_bufs field inside Packrat, which I found surprising. This doesn't work on Cosmo.

Now, granted, the entire spd command won't work on Cosmo per se, but this is relevant because rendmp uses spd internally, to check for DIMM presence. This is a Gimlet-ism we're going to have to clean up.

[rmustacc]

Is this a dup of #568?