lpm-levels: Compute minimum residencies for LPM levels

Minimum residency of current level is maximum residency of previous
level + 1. If none of the previous levels are enabled, minimum
residency of currenct level is time_overhead of current level.

Minimum residencies are used for New LPM level selection using
prediction logic.

Change-Id: I5e69a847d78d14ecbb7caeac383287a1897f7ce8
Signed-off-by: Raju P.L.S.S.S.N <rplsssn@codeaurora.org>