This eliminates the difficult to follow mapping of a string list. It
moves numbers from "#define" into (more) debuggable enums. More
generally, it follows the trend of moving more data into a more central
mechanism.
The help output is a little worse: " " is not rendered well, and there
are duplicate entries, but that will be fixed in a followup.
We've been maintaining top(1) for a long time, and the upstream
hasn't existed/been used in similarly as long. Make it clear that we own
top(1)
Tested with 'make universe'. Everything passed except MIPS which failed
for unrelated reasons. Install also tested for amd64.
Reviewed by: sbruno
No objections: imp, mmacy
Differential Revision: https://reviews.freebsd.org/D15387
