top(8): use designated initializers for sorted_state[]

Also correct comments for individual state, duplicating the S* constants
descriptions from sys/proc.h [*].

Reviewed by: kevans (previous version)
Noted by: Mark Millard <marklmi@yahoo.com> [*]
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D40607