anv: Implement VK_KHX_external_memory_fd

anv: Implement VK_KHX_external_memory_fd

This commit just exposes the memory handle type.  There's interesting we
need to do here for images.  So long as the user doesn't set any crazy
environment variables such as INTEL_DEBUG=nohiz, all of the compression
formats etc. should "just work" at least for opaque handle types.

v2 (chadv):
  - Rebase.
  - Fix vkGetPhysicalDeviceImageFormatProperties2KHR when
    handleType == 0.
  - Move handleType-independency comments out of handleType-switch, in
    vkGetPhysicalDeviceExternalBufferPropertiesKHX.  Reduces diff in
    future dma_buf patches.

Co-authored-with: Chad Versace <chadversary@chromium.org>
Reviewed-by: Chad Versace <chadversary@chromium.org>