ram: rk3399: Add LPPDDR4-400 timings inc

ram: rk3399: Add LPPDDR4-400 timings inc

LPDDR4 initialization start with at board selected frequency
and then it switches into 400MHz and 800MHz simultaneously to
make the proper sequence work on each channel with associated
training.

So, add LPDDR4-400 timings inc file in driver area so-that
these timings will take during LPDDR4 initialization phase.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: YouMin Chen <cym@rock-chips.com>
Reviewed-by: Kever Yang <Kever.yang@rock-chips.com>