sched/balancing: Remove reliance on 'enum cpu_idle_type' ordering when iterating...

sched/balancing: Remove reliance on 'enum cpu_idle_type' ordering when iterating [CPU_MAX_IDLE_TYPES] arrays in show_schedstat()

show_schedstat() output breaks and doesn't print all entries
if the ordering of the definitions in 'enum cpu_idle_type' is changed,
because show_schedstat() assumes that 'CPU_IDLE' is 0.

Fix it before we change the definition order & values.

[ mingo: Added changelog. ]

Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20240308105901.1096078-3-mingo@kernel.org