hw/misc: Add Microchip PolarFire SoC DDR Memory Controller support

hw/misc: Add Microchip PolarFire SoC DDR Memory Controller support

The PolarFire SoC DDR Memory Controller mainly includes 2 modules,
called SGMII PHY module and the CFG module, as documented in the
chipset datasheet.

This creates a single file that groups these 2 modules, providing
the minimum functionalities that make the HSS DDR initialization
codes happy.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 1603863010-15807-3-git-send-email-bmeng.cn@gmail.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>