ram: rk3399: Add LPPDR4 mr detection

ram: rk3399: Add LPPDR4 mr detection

Like data training in other sdram types, mr detection need
to taken care for lpddr4 with looped rank and associated
channel to make sure the proper configuration held.

Once the mr detection successful for active and configured
rank with channel number, the same can later reused during
actual LPDDR4 initialization.

So, add code to support for it.

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>