msf2: Add Smartfusion2 SoC

Smartfusion2 SoC has hardened Microcontroller subsystem
and flash based FPGA fabric. This patch adds support for
Microcontroller subsystem in the SoC.

Signed-off-by: Subbaraya Sundeep <sundeep.lkml@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20170920201737.25723-5-f4bug@amsat.org
[PMD: drop cpu_model to directly use cpu type, check m3clk non null]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
