anv: Emulate texture swizzle in the shader when needed

Now that we have the descriptor buffer mechanism, emulated texture
swizzle can be implemented in a very non-invasive way.  Previous
attempts all tried to extend the push constant based image param
mechanism which was gross.  This could, in theory, be done much faster
with a magic back-end instruction which does indirect MOVs but Vulkan on
IVB is already so slow this isn't going to matter much.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104355


Cc: "19.1" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
(cherry picked from commit d2aa65eb)