ARM: tegra: Use DT /cpu node to detect number of CPU core

SCU based detection only works with Cortex-A9 MP and it doesn't
support ones with multiple clusters. The only way to detect number of
CPU core correctly is with DT /cpu node.

Tegra SoCs decided to use DT detection as the only way and to not use
SCU based detection at all. Even if DT /cpu node based detection
fails, it continues with a single core

Signed-off-by: Hiroshi Doyu <hdoyu@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>