ARM: tango4: Initial platform support

Support Sigma Designs ARM-based (specifically, Cortex-A9 MPCore r3p0)
Tango4 "Secure Media Processor" platforms: smp8756, smp8758, smp8759
(8756 is single-core, the latter are dual-core).

Note: 8758 vs 8759: same chip, different package.

Support for older MIPS-based platforms can be found elsewhere:
https://github.com/mansr/linux-tangox



Signed-off-by: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>
Reviewed-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>