tegra124: Add PSCI support for Tegra124

This is based on Thierry Reding's work and uses Ian Campell's
preparatory patches. It comes with full support for CPU_ON/OFF PSCI
services. The algorithm used in this version for turning CPUs on and
off was proposed by Peter De Schrijver and Thierry Reding in
http://thread.gmane.org/gmane.comp.boot-loaders.u-boot/210881

. It
consists of first enabling CPU1..3 via the PMC, just to powergate them
again with the help of the Flow Controller. Once the Flow Controller is
in place, we can leave the PMC alone while processing CPU_ON and CPU_OFF
PSCI requests.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>