Do not power off the CPU1 since there is no way to wake it up
(wake-up is causing CPU0 reset as well duo to HW bug). Quote from errata
Ref #13 [In power saving mode, both cores must be powered off]:
"When Core 0 is on and Core 1 is in power-off state, a Core 1
wake-up resets Core 0 as well and puts Core 0 back to ROM".

To overcome described HW bug instead of powering the CPU off, let it
reach WFI instruction, which is invoked by generic psci_do_cpu_off
function after platform handler finishes. This will put the core in low
power state and give a chance to wake it up.

Before this change, after running secondary kernel via kexec, only one
core was up, now both cores are up.

Change-Id: I87f144867550728055d9b8a2edb84a14539acab7
Signed-off-by: Grzegorz Jaszczyk <jaz@semihalf.com>
Reviewed-by: Kostya Porotchkin <kostap@marvell.com>