CP-5599: Allocate vGPU on VM start

Find a pGPU on which the vGPU can be allocated as part of the Vgpuops
performed by VM.start.

The strings used for the platform map have been added to
Xenops_interface to avoid transcription errors.

Imported from xen-api.git 5676980f5f75c54f5fc0f39b61445f5c8f4b689a

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
Imported-by: John Else <john.else@citrix.com>

xc/xenops_server_xen.ml

@@ -905,13 +905,14 @@ module VM = struct
 					| Cirrus -> Device.Dm.Cirrus, None
 					| Standard_VGA -> Device.Dm.Std_vga, None
 					| Vgpu ->
-						List.iter (fun (k,v) -> if try String.sub k 0 4 = "vgpu" with
-						Invalid_argument _ -> false then
-							debug "VGPU config: %s -> %s" k v) vm.Vm.platformdata;
 						let vgpu =
 							try
-								Some (List.assoc "vgpu_pci_id" vm.Vm.platformdata,
-								      List.assoc "vgpu_config" vm.Vm.platformdata)
+								let vgpu_pci = List.assoc Xenops_interface.vgpu_pci_key vm.Vm.platformdata
+								and vgpu_config = List.assoc Xenops_interface.vgpu_config_key vm.Vm.platformdata in
+								debug "VGPU config: %s -> %s; %s -> %s"
+									Xenops_interface.vgpu_pci_key vgpu_pci
+									Xenops_interface.vgpu_config_key vgpu_config;
+								Some (vgpu_pci, vgpu_config)
 							with Not_found -> failwith "Missing vGPU config in platform data" in
 						Device.Dm.Vgpu, vgpu
 				in