Create local C library implementation (1/2) ...

- This change is split into two separate patches in order to
  simplify the history as interpreted by 'git'. The split is
  between the move/rename and addition of new files.
- Remove dependency on toolchain C library headers and functions in
  order to ensure behavioural compatibility between toolchains.
- Use FreeBSD as reference for C library implementation.
- Do not let GCC use default library include paths.
- Remove unused definitions in modified headers and implementations.
- Move C library files to 'lib/stdlib' and 'include/stdlib'.
- Break std.c functions out into separate files.

Change-Id: I91cddfb3229775f770ad781589670c57d347a154

Enable third party contributions ...

- Add instructions for contributing to ARM Trusted Firmware.

- Update copyright text in all files to acknowledge contributors.

Change-Id: I9311aac81b00c6c167d2f8c889aea403b84450e5

Treat compiler, assembler and linker warnings as errors ...

Change-Id: I56284ebf63bef99de1beb4fd86e2d8b6a7962ac0

Generate build products in sub-directories ...

A single binary can be compiled using a command such as:
  make CROSS_COMPILE=aarch64-none-elf- bl1

Also make use of brackets consistent in the Makefile.

Change-Id: I2180fdb473411ef7cffe39670a7b2de82def812e

ARMv8 Trusted Firmware release v0.2