ram: rk3399: Fix dram setting to make dram more stable

There are some code different with rockchip vendor code which may lead
to different bugs, including:
1) Fix setting error about LPDDR3 dram size ODT.
2) Set phy io speed to 0x2.
3) Fix setting error about phy_pad_fdbk_drive.
4) Fix setting error about PI_WDQLVL_VREF_EN

Signed-off-by: YouMin Chen <cym@rock-chips.com>
Signed-off-by: Kever Yang <kever.yang@rock-chips.com>