build from: c7d3dcd3f0 dram_init: rk3506: update ddrbin to v1.02 update feature: 1. support rk3502 2. add 750MHz support.(Supported frequencies include 451 589 750MHz) Signed-off-by: Tang Yun ping <typ@rock-chips.com> Change-Id: If958f8c3b15efba396c29607083bf9b63096add6