Make attrmap able to alter memory attributes as well

[mmicko]

It was not possible to alter memory attributes with attrmap.

By using selected_members iterator instead we are covering all as we already do plus memories.

attrmap_apply was removed from processes block, but also used a chance to cleanup and use selected_processes to handle rest of changes needed

[KrystalDelusion]

Since we are touching this file we should also review the deprecation warning on it. From #4768:

Note:
Design::selected_whole_modules() is marked deprecated because I'm not convinced attrmap should be ignoring boxes, even though that is the current behaviour.

Design::selected_whole_modules() previously iterated over all wholly selected modules while silently ignoring any boxed modules. Most of the previous uses of this method were updated in #4768 to use the equivalent, Design::selected_unboxed_whole_modules(), but attrmap wasn't because I wasn't sure how it should handle boxes.

For comparison, setattr uses Design::all_selected_modules() which includes boxes. wbflip specifically says "Blackbox cells are not effected by this command" and uses Design::selected_modules(RTLIL::SELECT_ALL, RTLIL::SB_EXCL_BB_ONLY). blackbox uses Design::selected_whole_modules_warn(true) to include whiteboxes but warns on blackboxes and partially selected modules.

For the non -modattr mode it is using the default Design::selected_modules() which includes partially selected modules, and warns on any boxes in the selection. If we end up including boxes for -modattr we may also want to change the other one to match.