Export NvSciBuf from Vulkan SC

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