Change how PGPU.set_GPU_group is called via the CLI

Instead of

  xe pgpu-set-gpu-group uuid=... gpu-group-uuid=...

a user now needs to call

  xe pgpu-param-set uuid=... gpu-group-uuid=...

for consistency with other CLI setters.

Signed-off-by: John Else <john.else@citrix.com>
Merge pull request #1445 from johnelse/pgpu-cli-tweak

Change how PGPU.set_GPU_group is called via the CLI