Implement GPU support

[muhamadazmy]

Limitations:

• We start by supporting only one (and only one) GPU for now, while keeping in mind that more GPU can be available in zos node in the future

Changes

• Identify and list all attached GPUs
• On registration, a node need to update its set of features on the chain (depends on chain change extended Node features  tfchain#720)
• ZMachine can have an extra gpu flag (list of GPUs)
  • This is only accepted if node is dedicated (otherwise an error)
  • A GPU can be only used by one ZMachine
• Expose the gpu device to the VM (based on research here GPU Support #1293 (comment))

[muhamadazmy]

Sub-tasks

will be updated regularly

• Identify GPU devices (scan the system PCI and filter via class, then figure out the vendor/device names