Define NVX_device_generated_commands handles only when that extension exists.

After Vulkan SDK 1.2.135 (currently used in Fuchsia tree),
VK_NVX_device_generated_commands is renamed to VK_NV_... .

This change modifies the handle definition to make sure that
we only refer to these handle types when the NVX extension exists.

Change-Id: Ib1063f7d5e3b6efefee2bc643e4cef58fbd8a39f
1 file changed