ARM: multi_v7_defconfig: Enable Exynos5420 Multi-Cluster PM support

ARM: multi_v7_defconfig: Enable Exynos5420 Multi-Cluster PM support

The Exynos5420 cluster power management support allowing Exynos
5420/5422/5800 machines to power up and down the secondary CPUs.

Without this option enabled, the secondary CPUs are not brought
up on boot and the following error is shown:

CPU0: thread -1, cpu 0, socket 0, mpidr 80000000
Setting up static identity map for 0x40938e90 - 0x40938f28
ARM CCI driver probed
CPU1: failed to boot: -38
CPU2: failed to boot: -38
CPU3: failed to boot: -38
CPU4: failed to boot: -38
CPU5: failed to boot: -38
CPU6: failed to boot: -38
CPU7: failed to boot: -38
Brought up 1 CPUs

Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Olof Johansson <olof@lixom.net>