cpuidle:powernv: Add helper function to populate powernv idle states.

cpuidle:powernv: Add helper function to populate powernv idle states.

In the current code for powernv_add_idle_states, there is a lot of code
duplication while initializing an idle state in powernv_states table.

Add an inline helper function to populate the powernv_states[] table
for a given idle state. Invoke this for populating the "Nap",
"Fastsleep" and the stop states in powernv_add_idle_states.

Signed-off-by: Gautham R. Shenoy <[email protected]>
Acked-by: Balbir Singh <[email protected]>
Acked-by: Rafael J. Wysocki <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>