arm: Add support for Jetson TK1 board

arm: Add support for Jetson TK1 board

The Jetson TK1 board uses the NVIDIA K1 processor, namely the Tegra124.
The CPU has 4 Cortex-A15 cores and a low-power companion core which we
do not support, though. This SoC apparently contains all virtualization
features we need, specifically full SMMU coverage of I/O devices.

For now, board support is similar to the Banana Pi: We replicate UART
and SMP/PSCI features and add some configs (only one for both demos as
only one UART is accessible).

Open issues, besides adding SMMU support, are managing the access to the
so-called legacy Interrupt controller of the K1 (an additional stage
between devices and GIC) and sub-page access control to various devices
(same issue as with the Allwinner A20). Also, it becomes clearer than
ever that we urgently need to refactor the UART layer as well as
SMP/PSCI support to reduce duplications.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>