ARM: tegra: Always boot CPU in ARM-mode

CPU always jumps into reset handler in ARM-mode from the Trusted
Foundations firmware, hence let's make CPU to always jump into kernel
in ARM-mode regardless of the firmware presence. This is required to
make Thumb-2 kernel working with the Trusted Foundations firmware on
Tegra30.

Tested-by: Robert Yang <decatf@gmail.com>
Tested-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>