spirv: Add vtn_mode_to_address_format()

spirv: Add vtn_mode_to_address_format()

Handles all the modes and we can use it in combination with
nir_address_format_to_glsl_type() to replace the
vtn_ptr_type_for_mode() helper.  Since the new helper is more generic,
moved the assertions from the old one to the call sites.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>