Use the correct value of hz (stathz if it is nonzero) for
interpretion of dk_time[] and cp_time[] in iostat.c. Avoid
multiple conversions of this value in iostat.c and vmstat.c
iostat.c:
Implement the display of cp_time[CP_INTR]. Fix the display
of cp_time[CP_IDLE] (the display was always null because
cp_time[CP_INTR] == 0 was displayed instead).
systat.1:
Document the display of cp_time[CP_INTR].
vmstat.c:
Implement the display of cp_time[CP_INTR].