Export NvSciSync from Vulkan SC

In the Vulkan SC Specification, VK_NV_external_sci_sync2 defines a feature to export an NvSciSyncObj. In Vulkan SC terminology, “export” indicates the Vulkan SC driver allocates and manages the NvSciSyncObj instead of application. To keep the interfaces symmetrical with other NVIDIA DriveOS UMDs, this feature is always disabled. Applications can use the vkGetPhysicalDeviceFeatures2 API by passing a VkPhysicalDeviceExternalSciSync2FeaturesNV struct to query the enablement of this feature.