CP-5812: Remove a no-longer-needed check

We now allow VGPU creation even if the type is not one of those allowed
by the group.

Signed-off-by: John Else <john.else@citrix.com>
CP-5812: Fix the VGPU_type <-> PGPU relation

Signed-off-by: John Else <john.else@citrix.com>
CP-5812: Add a helpful comment for future explorers

Signed-off-by: John Else <john.else@citrix.com>
CP-5812: Add a relation between a PGPU and its enabled VGPU_types.

Signed-off-by: John Else <john.else@citrix.com>