Updates for ARM Trusted Firmware tag v1.0

* New load address for plat-vexpress,fvp
* Entry vector extended with system_off and system_reset
  entries
Add documentation for ARM Trusted Firmware

Adds documentation how to compile and run with
ARM Trusted Firmware.
Makefile variables $(*-dir) should not have a trailing slash

As a general rule, Makefile variables that are directories should not have
a trailing slash, and should be used as: $(some-dir)/some-file rather than
$(some-dir)some-file. This is more readable.