anv/image: Separate modifiers from legacy scanout

anv/image: Separate modifiers from legacy scanout

For a bit there, we had a bug in i965 where it ignored the tiling of the
modifier and used the one from the BO instead.  At one point, we though
this was best fixed by setting a tiling from Vulkan.  However, we've
decided that i965 was just doing the wrong thing and have fixed it as of
50485723523d2948a44570ba110f02f726f86a54.

The old assumptions also affected the solution we used for legacy
scanout in Vulkan.  Instead of treating it specially, we just treated it
like a modifier like we do in GL.  This commit goes back to making it
it's own thing so that it's clear in the driver when we're using
modifiers and when we're using legacy paths.

v2 (Jason Ekstrand):
 - Rename legacy_scanout to needs_set_tiling

Reviewed-by: Daniel Stone <daniels@collabora.com>