tools: ynl: cli: Display enum values in --list-attrs output

tools: ynl: cli: Display enum values in --list-attrs output

When listing attributes with --list-attrs, display the actual enum
values for attributes that reference an enum type.

  # ./cli.py --family netdev --list-attrs dev-get
  [..]
    - xdp-features: u64 (enum: xdp-act)
      Flags: basic, redirect, ndo-xmit, xsk-zerocopy, hw-offload, rx-sg, ndo-xmit-sg
      Bitmask of enabled xdp-features.
  [..]

Reviewed-by: Nimrod Oren <noren@nvidia.com>
Signed-off-by: Gal Pressman <gal@nvidia.com>
Link: https://patch.msgid.link/20251118143208.2380814-4-gal@nvidia.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>