nir: Add nir_address_format_logical

nir: Add nir_address_format_logical

An address format representing a purely logical addressing model.  In
this model, all deref chains must be complete from the dereference
operation to the variable.  Cast derefs are not allowed.  These
addresses will be 32-bit scalars but the format is immaterial because
you can always chase the chain.  E.g. push constants in anv.

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