gdb integration doesn't support AVX-512

[khuey]

Something I noticed while mucking around with the PKRU stuff yesterday is that none of our gdb integration supports the AVX 512 registers (the ZMMs and XMM16+). I don't plan to implement this but I want it on file.

[theIDinside]

Just adding this comment here to signal that I'm working on this feature (I don't have assign assignee-privileges :stuck_out_tongue:)