Add global VM platform values for vGPU

Adapted from clearwater-lcm changeset dc899a7

Signed-off-by: John Else <john.else@citrix.com>
CP-5599: Vgpuops filters for PCI-passthrough VGPUs

Updated the logic for original VGPU functionality (full-GPU-passthrough) to
only passthrough the PCIs when appropriate (full-GPU-passthrough).

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
CP-5599: Remove unused (and ambiguous) function

With the introduction of vGPU alongside GPU-passthrough (both of which are
termed VGPUs in xapi) this function is now ambiguous. It's also unused in the
codebase and so has been removed.

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
CP-5599: Factor out PCI-passthrough VGPU creation

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
CP-5599: Add internal_conf to VGPU_type

This has been added as a (string * string) map to be most forwards compatible
and will currently be used to hold the path to the config file that needs to be
passed to the NVIDIA VGX plugin.

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