Add Xilinx to acknowledgements file ...

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>

TLK-D documentation and add NVIDIA to the Acknowledgements file ...

Include TLK Dispatcher's documentation and add NVIDIA to the
Acknowledgements file. TLK is now a supported Trusted OS with
the Trusted Firmware.

Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>

Build system: Fixes #2: Add multi-platform support ...

Move all explicit platform or architecture specific references
into a new platform.mk file that is defined for each platform.

Change-Id: I9d6320d1ba957e0cc8d9b316b3578132331fa428
Signed-off-by: Ryan Harkin <ryan.harkin@linaro.org>

Enable third party contributions ...

- Add instructions for contributing to ARM Trusted Firmware.

- Update copyright text in all files to acknowledge contributors.

Change-Id: I9311aac81b00c6c167d2f8c889aea403b84450e5