anv: modify the internal concept of format to express multiple planes

anv: modify the internal concept of format to express multiple planes

A given Vulkan format can now be decomposed into a set of planes. We
now use 'struct anv_format_plane' to represent the format of those
planes.

v2: by Jason
    Rename anv_get_plane_format() to anv_get_format_plane()
    Don't rename anv_get_isl_format()
    Replace ds_fmt() by fmt2()
    Introduce fmt_unsupported()

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>