driver: ram: rockchip: rk3399: add lpddr4 support

Select rk3399-sdram-lpddr4-100.dtsi to initialize LPDDR4
at 50MHz, it will change clock frequency to 800MHz
after initialization is complete.

Chang

driver: ram: rockchip: rk3399: add lpddr4 support

Select rk3399-sdram-lpddr4-100.dtsi to initialize LPDDR4
at 50MHz, it will change clock frequency to 800MHz
after initialization is complete.

Change-Id: I803ed2c809f17bbea40f379194bce548adc338ea
Signed-off-by: YouMin Chen <cym@rock-chips.com>

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