Remove unneeded assertion

assert_VGPU_type_allowed now calls assert_VGPU_type_enabled

Signed-off-by: John Else <john.else@citrix.com>
Make free PCI functions check a bit more cautious

Signed-off-by: John Else <john.else@citrix.com>
Add API call PGPU.set_enabled_VGPU_types

Signed-off-by: John Else <john.else@citrix.com>
Make PGPU.enabled_VGPU_types settable on the CLI

Signed-off-by: John Else <john.else@citrix.com>
Garbage collect unused and unsupported VGPU_types

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
Simplify VGPU_type GC with new datamodel relations

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>