Enable third party contributions ...

- Add instructions for contributing to ARM Trusted Firmware.

- Update copyright text in all files to acknowledge contributors.

Change-Id: I9311aac81b00c6c167d2f8c889aea403b84450e5

FDTs for v5.2 Foundation model ...

- The Foundation FVP is a cut down version of the Base FVP and as
  such lacks some components.
- Three FDTs are provided.
  fvp-foundation-gicv2legacy-psci:
    Use this when setting the Foundation FVP to use GICv2. In this
    mode the GIC is located at the VE location, as described in the
    VE platform memory map.
  fvp-foundation-gicv3-psci :
    Use this when setting the Foundation FVP to use GICv3. In this
    mode the GIC is located at the Base location, as described in the
    Base platform memory map.
  fvp-foundation-gicv2-psci :
    Use this when setting the Foundation FVP to use GICv3, but Linux
    is expected to use GICv2 emulation mode. In this mode the GIC is
    located at the Base location, but the GICv3 is used in GICv2
    emulation mode.

Change-Id: I9d69bcef35c64cc8f16550efe077f578e55aaae5