Sharing DDR3 memory between two sources
You should look at the SoC and Zync devices from Altera and Xilinx. These chips offer ARM9 processors merged with FPGA fabric. This allows you to setup a single DDR3 interface, but have both the FPGA and CPU's access it via internal multi-port DDR3 controllers.

Cyclone V SoCs: Lowest System Cost and Power

Zynq-7000 All Programmable SoC