anv: Don't reject Android image format if external props not supplied
What does this MR do and why?
anv_GetPhysicalDeviceImageFormatProperties2
returns 'not supported' if an
Android hardware buffer external memory handle type is specified, but no
external image format properties output struct is supplied. This struct is
optional, so we should populate it if present, but return successfully
either way.
This fixes an error when using ANV with hwui, which otherwise prevents the system from booting.1