top(1): another pass of cleanup

top(1): another pass of cleanup

- avoid the need to call a function to get size of known array. I'll
likely re-arrange some of the indirect in a later to avoid the magic
constants.
- use correct type
- add const
- replace caddr_t with void*. This corrects an alignment warning.
- remove duplicated include from immediately prior commit

Under base clang we're now down to:
- 3 warning in top.c, 1 warning in mahcine.c,  4 warning in display.c,
- 1 warning in utils.c

Tested with base clang, gcc7, gcc9, base gcc (mips)