arm: use cpu scale value derived from energy model

To make sure that the capacity value of the last element of the capacity
states vector of the energy model (EM) core (MC) level is equal to the
cpu scale value, use this capacity value to overwrite the cpu scale
value preeviously derived from the Cpu Invariant Engine (CIE).

This patch is necessary as long as there is no complete EM support in
device tree.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>