We already saved different entity attributes depending on the entity
type and an is_parameter flag. This unifies handling of different entity
types and introduces normal, method, parameter, label and
compound_member entities.

Make sure all types are in the global type list, remove type_walk_prog
which was a strange alternative to type_walk attempting to not miss
types not in the global list.

This should fix problems with uninitialized backends when
be_get_backend_param() wasn't called also calls be_lower_for_target if
the user hasn't done so yet.

get_backend_irg_list - none of our backends uses it and in the future
                       the backend should drive the compilation and not
                       give hints to a generic driver
reg_class_alignment  - unused

This fixes opt/fehler206.c.

before we only tested, if we produce an output that is used as as input
of any schedule node in between. This missed the case where you have
unscheduled utility nodes like Sync in between.

The interface was really inefficient and shouldn't be used like that.
So simply don't provide functions that make inefficient code convenient.

We missed the case where transform_node created a node that
computed_value or equivalent_node would catch

It was a strange feature only inspired by the lazyness of some frontend
developer (=me)

they were in lower_mode_b but just generically apply to all Mux(c, 0, 1)